Buy a Pake or a Surly steel frame, swap the parts over from the Allez and then sell the Allez frame on Craiglist and basically end up spending a couple hundred bucks and getting a good all around bike!

Any bike can be used as a commuter. The cheapest solution would be to get the beam rack and change your seatpost to something non carbon fiber. You should also be able to attach a rack using p-clips. I am unsure about fenders and what would fit on your bike.

The second choice would be to get something used. Check out craigslist, coops, pawn shops, lbs that sell used, auctions, and garage sales. You could probably snatch something for not much money and purchase fenders, rack, and whatever else you need. My preference is the mid 80's - 90's rigid MTB's.

I honestly think a new bike such as a touring or cross bike would be a bit much just to have for commuting. However if you do plan on taking some kind of tour then get one.

Id do what I currently do now.. Bring in a weeks worth of clothes to work by car on my day off, commute wearing shorts, gloves, clipless shoes and a DriFit shirt..In the 1 year, 9 days 4,277.5 miles ive owned my Allez sport ive never found a problem with pinch flats or warped rims and I run between 183-195lbs..If you really want bags shell handle them just fine . Never tried fenders, I cant stomach the looks of them but if you have a rack it keeps you from getting a mud stripe up your back..Ive had no problems with the seals and bearings from rain either.. Id rather commute fast and lite so things have changed a bit from that pic..

I don't think you need a different bike. Get a backpack like Deuter Aircomfort 28L. No more sweaty back problem. Then you can enjoy riding.

Where does the OP live?

Try going no fenders in a 35F hard rain for a 20+ mile commute. If that weather is a possibility, fenders are pretty much a necessity. And if the OP still wants to ride a "fast" bike, he's going to need two. Or more.

And no backpack in the world can avoid creating overheating issues when temperatures reach 90-100F or maybe even hotter with any humidity. When temps like that make it necessary for you to be able to dump heat, covering up a large surface that would otherwise be wide open to ventilation is not a good idea.

I'll take the 'fast-light-wet-ass" commute any day rather than putting fenders, racks and other crepe on my Giant.

I've often wanted to ride sans-shirt when we have a hot humid day. I can't figure why more folks don't because it'd be a lot cooler. The only thing that has stopped me is that I would be the only person I've ever seen w/o a shirt on a bike, since I was about 10 years old.

Unnecessary expense. That's why not.

Understood.

Although having it for the clock would be nice. The rest is just trivia to me.

Sporty hybrid.

I commute on a 2005 Allez Sport. I added the Tubus Logo rack and some Ortlieb Backrollers this winter. I love my set up. I was commuting on a Rockhopper before but I was very surprised at the durability of the Allez. My commute takes me over four sets of train tracks and down some pretty nasty roads. I've put about 1400 miles on the Allez and have only had two flats. I'm sticking with my Allez.

You have a much simpler option -- just buy a large seatbag like a Carradice Barley or Pendle. I have commuted 22 miles round trip for nearly four years using a Barley to carry all of my gear. I commuted on a racing frame for more than two years using the Barley. Two years ago, I bought a touring frame but continue to use the Barley. I briefly installed a rear rack and considered getting panniers, but decided after a short while that the Carradice bag was all I needed to carry my gear and I removed the rack.

If it were my commute, I'd add the rack & put the backpack on your Allez. Then I'd look into getting wider tires & fenders. Full Fenders are great & I'd recomment those if they'll fit on your bike, but even those little clip on ones will make a difference. Wider tires will give you a more comfortable ride. (Also lower Tire pressure will be more comfortable as well. If you are currently inflating your tires to the max PSI, try lowering that a bit to smooth out the ride.) The fneders & rack can move over to a new bike if you do pick up a commuter in the future. As far as the puddles go, I haven't ever really heard of anyone carrying a bike over them. As you get to know your commuting route, you may find some puddles that hide large potholes in the pavement. Those you may want to ride around, but other than that, the fenders should keep the spray down from the rest of them.

because that nasty money burns holes in their pockets?

I'd get another bike...but if you don't want to do that, put some sks raceblade fenders and a rack on your allez and have a ball.

No real new info here- most people have already offered every possible opinion, but to agree with some...
Make sure you get a bike youenjoy, it makes commuting more fun. I had a similar issue, i was looking to buy a bike (one bike) to do everything. I didn't have enough $$ for more than one. I wanted a racing bike with drop bars b/c I wanted to go for fitness rides on the weekends, but still have a fun commute. I heard the same thing about racing bikes- no good for commuting. It was suggested I get a cyclocross bike, which offers the best of both worlds. Sturdy, able to attach rack, fast, sleek. Brand new, they cost a lot more than I had, but after some patient searching I picked up a great bike on craigslist for $400. I haven't looked back since. It's a blast whenever I ride. Good luck, have fun.

You should try it. Maybe you'll start a fad.

If you need help, come visit me in June. I'll show you how to do it.

Used touring bike with fenders+rack for rainy days, new racing bike with clamp-on or large seat bag on nice days.

My rainy day commuter is a 1983 Trek 500 with fenders and a rear rack. I need the rack for my son's Burley Kazoo trailer bike anyway, so I put panniers on it.

I store extra changes of clothes at work, so on some nice days I commute on my nicer road bike without any bags; other days I use a clamp-on rack. I keep a messenger bag + U-lock at work in case I need to carry anything home or need to run an errand during the day without a rack.

Trivia can be fun:

Total mileage (can also be used for maintenance intervals)
Travel time (timing yourself is a good way to develop conditioning)
temperature - not that you can do anything about it, but it's nice to know sometimes
cadence - again, it's about conditioning and training for some of us
clock - goes without saying

I have a small, unassuming computer on my stem that provides these and other data about my bike, my ride, and my environment - it all enhances my experience - for $25, it's worth it to me

If, as you say, you are serious about commuting, I would recommend a separate bike set up for commuting. I lucked out and got an older steel frame hardtail Mountain Bike - CHEAP!, and over the course of the last 3 years have outfitted it with narrower street tires (Michelin 1.75 wide Country Rocks), a rack, fenders, pump, and panniers. I used a backpack for a long time, and must retract any statements about backpacks being fine for commuting, at least for me. The rack and panniers are MUCH more comfortable and easier to use. Some days I ride one of the road bikes if I don't have any cargo, but I enjoy the commuter immensely too, in it's own way, and never worry about having to jump a curb, or take to the dirt if the truck coming up behind me looks like it wants my part of the lane(shoulder, what shoulder?), even with my 260# on board. I average 2mph slower on the commuter, that's the main difference.

Another vote for craigslist. I found an older Schwinn Moab with rear rack, panniers, cheapo lights and a bottle of chain lube for $90. I rode it yesterday and it comes in handy for errands where I have to lock up and leave it.

You have already answered your own question. If the Allez has rack mounts, put a rack on it and ride it to work every day. You could always remove the rack if you wanted to race it.
By doing this, you will get an idea of going car-less, on the cheap. It will also give you a better idea of what you need/want in a second bike, ie, fenders, more braze on's, room for bigger tires.

When I got back to riding I bought a Surly CC and stuck 23 tires on it. I rode it in fast group rides, and back and forth to work. I liked it, still do. Now it's my truck, I am almost car free, about 95% free.
I also bought a better race type bike, lighter, smother, and quicker, but not much faster. Oh wait maybe that is me!