I'm a big fan of backpack commuting, especially since I got a pack from the folks at wingnutgear.com at a bike show. The pack is in need of repair so it's off at their shop. I started commuting to a new job this week, though, so I brought out the panniers and trunk my wife uses for a rare commute and that I've used many a time (esp. the panniers -- I've had them for 10 years!) for hauling stuff from, say, a farmer's market. I put the nifty QR full rack (yes they exist) on my folder and it's been great. My only complaint is that with the short chainstays on my folder, I have the pannier (I'm only using one) very far back on the rack to avoid the back of my shoe, so far, in fact, that the pannier looks to be brushing the tire once in a while. Not sure what to do about that, though I think the tire is none the worse wear so a little duct tape on the pannier could do the trick.

The only thing I dislike about panniers is that they make me carry more useless crap

When you are the human sweat machine, panniers are the only choice!

I'm thinking that in the summer even with my backpack fixed I'd revert to this setup b/c I really do sweat a lot!

I finally switched to a pannier this fall after 10 years with a timbuk2 messenger bag, and I must say I'm sold. I'm using the arkel commuter. Sure the capacity and load bearing qualites of the pannier are great but I've been surprised to find more postive aspects to this than I had anticipated, such as:

1. No more sweaty back. (as has been stated)
2. No more sore neck and shoulder (especially when I lug my laptop)
3. My jackets and layers ventilate the way the are supposed to becuase they aren't being squeezed by my bag, the result is a much more comforatble ride and far easier to use vents to regulate my body temp.
4. Getting out of the saddle to pedal seems so much easier, and in general peddling and breathing is easier.
5. I seem to have better balance and control on icy/snowy surfaces. My torso is free to move and shift without the weight on it. Since the weight has been transfered it creates a overall lower overall center of gravity whcih helps too. The off-center load is not an issue at all.

The Arkel is a solid design, perfect for my needs, I've yet to find a downside.

I must admit I resisted it for years, becuase I thought I was being a tough guy, and I was so cool, and it was geeky to have the rack and pannier. That was dumb. Going to the pannier was smart. I'm glad I did it.

I used to use a backpack on my commutes. With a sore lower back and the sweat that came with it I changed over to panniers. While I do find them useful, I feel a rack trunk is the best choice. Otherwise, I tend to haul everything including the kitchen sink. Not to mention the areo hit it caused me. Now I pack what I need for the day and call it good. This is entertaining when you can have a 15F morning and a 60F afternoon in Colorado.
I still use the backpack for around town errands. Panniers are used from time to time when I need to haul something to work.

I use a rack trunk with shoulder strap. Can just throw it over my back like a messenger back when in stores and out and about. Also I wrap the shoulder strap around the seat post, just in case I'm going super fast around a corner and the G forces cause the trunk to go flying off...

I was going to make some "fender skirts" out of plastic cutting sheets by cable tying them to the rack and mount a couple of small bags for when I didn't need large panniers. As it turns out I did not need fender skirts at this time. Something like that would keep bags from touching your wheel, you could cut up a plastic jug or something as well.

<knowing nod of the head as more posts emerge about the downside of backpack commuting>

Still, I can't wait for my backpack to be back from the maker (free repair, those guys are awesome -- they even called me to chat and let me know they're on the job). It's a super backpack for riding -- I've used it for centuries (has a slot for hydration bladder).

I'm with you.
I always used a backpack. Well about a month ago I got Topeak "MTX Beam Rack,Mtx dual side frame,MtX Trunkbag EXP, Rain cover, and I can not believe I got this a MTX DeFender. I am not a fender person.. And I love it.
It has far more room then I thought it would. I think it has more room the my backpack does.

Don't worry... I've back-pack commuted a lot, too, but only because the bikes I've used have not had racks. If I am carrying a laptop computer, hard-cover books or binders or more than 3kg of gear, I'll opt for the bike with racks and a rack bag or pannier. I've done centuries, too, with a backpack, but the sweat and heat issue remains.

Like most things cycling, go with what turns you wheels at any particular time

I'm a messenger bag user, primarily because I commute on one of three different bikes depending on my mood and the weather. Only one of the bikes has a rack, so much of the time I will need to use a backpack/mess bag any ways. If I commuted with a pannier on my bike with the rack I would have to transfer the tools, pump and spare tubes between different bags. I am very prone to forgetting to make the transfer, which following Murphy's Law would result in me having a flat or break down without tools. The other advantage I found is this way I only have to have one good quality water proof bag, and I think messenger bags are slightly less expensive than equivalent quality panniers.
Of course my load is usually fairly light, thermos of coffee, couple change of clothes, lock, tools, additional layers as necessary, so I don't find the pack uncomfortable. If I carried books and/or a computer I would use a pannier.
Craig

I've gotten over this by getting additional multi-tools that remain with whatever pack/pannier or bike I am using. In the ideal world, I would have a small underseat tool bag that remained with the bike, but the ideal world doesn't have thieves.

i agree with all your points except for this one- the reason i generally run with a backpack rather than panniers is that i can suspend the weight with my legs over bumps/ice ruts/potholes and actively shift the weight relative to the bike, rather than having it attached to the bike itself.

panniers are great for heavy loads, but i feel less manuverable with moderate loads in the pannier vs on my back.