My advice as one who has ridden a carbon fiber bike and an aluminum bike (own Ti, Alu, and steel now): do NOT pay carbon fiber price for an aluminum bike.

Yes, aluminum has its place and can be applied to make a nice bike. But it ain't carbon fiber. Point is, you can get a nice carbon fiber bike these days at a good price as more manufacturers make use of the material. I just see WAY too many full aluminum or aluminum/carbon stays frames going for ~$1500.

For example, this bike isn't worth $6300 whether Danilo Di Luca rides it, or it adds 2" to your anatomy. That's one extreme example, but I watched a 2004 Bianchi EV3 Alu/Carbon (stays are CF) go for $1200 yesterday. That's insane. For $1200, you could snag a full carbon Giant TCR, Specialized Roubaix, or possibly a new old stock high modulus CF Look for that. Many options at that price. Or a Ti bike on closeout (or maybe even new).

This is not to trash full aluminum or aluminum w/ carbon stays bikes. I scored a CAAD7 for $370 a couple months ago, and it'll see plenty of action on rainy days, on the trainer over the winter, and in crits during next year's race season. But I'll be on the Ti bike the rest of the time.

Aluminum is fine. Just don't pay out the wahzoo for it, because carbon fiber will almost always give you a smoother ride at or below the same weight. If you're going to put your miles in, I feel this is important. You'll be less beat up after a ride. That was a big plus for me last year going into this year. I don't think I could do that on an all aluminum bike.

Watch eBay for no less than a month every single day, and you'll get a good idea what bikes you are interested in go for. Go to an LBS and ride an aluminum bike and a CF bike to get a feel for the difference. Ask yourself how much more the CF is worth.