Why do you ride an aluminum bike?

cost

Cheaper than a full carbon.

When I bought my Cannondale, it was made really simple-the bike store gave their racing teams they sponsored big, sweet discounts on everything, including bikes.

X 10000000000000000000000000000000000000000

Because my dura-ace equipped QR Kilo was thousands less than a comparably equipped carbon bike. It fits me well, is comfortable, and the ride only starts getting "harsh" after 80-90 miles.

The biggest reason, though, was that, living in Minnesota, I needed one bike to use outdoors in the summer, and on the trainer in the winter. I didn't want to torque a carbon frame on a trainer for almost half the year.

Cost. you can buy a very well built aluminum bike with great components or a crap made carbon bike with shoddy components...

Well, a follow up question would be; what am I missing out on with an aluminum bike over carbon (or any other material)?

Many people say that aluminum is "harsher" to ride long compared to steel or carbon. I've ridden nice carbon bikes, and I admit that the ride is a little "softer" than my QR Kilo. The ride quality difference isn't something I even notice until 80 miles or so into a ride though, and I definitely don't notice it for an Olympic distance or sprint tri.

Oh, and you're also missing out on that nagging worry in the back of your mind that carbon riders get anytime there bike is dinged at all. The, is my bike gonna blow-up and catastrophically fail now that I've crashed it, or dropped it, etc.....

Cost here as well.....

But I also didn't want to get a full carbon bike and then be worried about when I am going to wreck, because I am a complete newb on the bike and I will wreck. I needed to have the assurance that I was riding something a little more sturdy in construction.....hence I ride a Cervelo P2SL and not a P2C.

Cost.  I'd love a full carbon bike!

 Because I can't afford a full carbon bike people who ride full carbon bikes are weenies.

I am riding on '07 Trek Equinox 9 that I bought last August and got a deal from LBS that I could not turn down. Bike is all Ultegra, which you can't get in 08 and on in Trek's line up. You can get the same frame with 105 group and it is '08 E7.
That was my first road bike ever. Since than, I trained and progressed ruther rapidly. I spent $200+ for pro fitting, went through several saddles, numerous minor adjustments of position and different set of aero bars. I settled with Vision aluminum base and ski bend extensions.
No race wheels, just those stock Bontrager Race Lite Aero.
The results. I raced 4 tris with it. I won my age group 3 out of 4 times, twice I posted the fastest bike split of the race (one sprint, one olympic distance), last two races I placed overall 4th and 3rd respectively.
Can you imagine the faces of people that had $7000-10000 bikes during both of my last races when they saw my bike on the rack next to theirs.
Progression on this bike in training for me was very obvious. This is my first year of structured plan of any kind, with no cycling background. This bike provided everything for me to master the basics. Since I don't have powermeter, I frequently use same out and back courses for field testing as well as measuring progress, while using HR and avg. speed, recording weather conditions. I went from an avg 20mph for a 20mi course last August, to 24.3 mph avg on a 25mi course two weeks ago. There is still a lot more room in improving my pedal stroke economy, tweaking my position, improving my "aerobic" engine.......
A set of race Zipps is coming this fall for next season.
As I plan on making 70.3 my main race distance, I will take another year of riding on this frame to help gain experience, learn more as to what I realy want to ride on. I may stick with it or I may get a carbon bike.
Don't know much about comfort as aluminum is all I know. My longest ride was 2:45 and I take those ok. Never ridden carbon frame that I can compare comfort. I am sure it is better in that regard as all pros ride on carbon.

i ride a mostly alum bike.

in the past i have owned/raced on: full carbon (2), full alum (1)

the bike i have now is alum with a carbon rear trianlge.

i ride it because:

1 it fits me amazingly well

2 it looks awesome

3 it is comfortable

4 i got a good discount

5 it is well built, which if you dont know a lot about bikes is a huge part of ride comfort. more so than material, the actual build of the bike will determine how it feels when you ride it. there are some lower end carbon bikes that ride like jackhammers, and some alum bikes that ride ilke silk. tire, bar choice, and wheels will all matter more in how the frame feels than frame material.

All you riders and your high tech materials. I ride steel.