I just came across a great (and highly biased–my favorite kind) of article comparing steel and carbon frames. The author is obviously trying to make a point of durability and customization over light weight, and he gets it across quite well.
For more proof of why the typical rider might want to avoid plastic bike frames, check out BustedCarbon.com or watch the amusing video below showing a completely unscientific, but easily repeatable, comparison between AL, steel and carbon frames. KAPUT!
For the record, I don’t really have anything against carbon fiber; in fact, I love the stuff. In the years I’ve been biking, I’ve ridden carbon handlebars, a rigid MTB fork, a carbon road fork, and a couple seatposts. I wouldn’t mind building up a 13lb all-carbon bike for occasional use, either. But, I still feel that steel is the ultimate material when you’re going for a combination of strength, durability, ride quality, price, and ease of manufacture.