I wonder why people don't use PLT that much. It has libraries, docs and tools, and its scheme(maybe thats the problem?). Its a cool environment, I like it very much.
Why don't more people use DrScheme, HTDP, etc.? This is a question about learning, culture, change, etc. more than any particular environment, method, etc.
Want to do billing? openid? you are out of luck. But having said that I'm experimenting with a site in PLT Scheme (and I know a couple that use Kawa as well).
Of course Clojure showing up may be part of the reason for that.