Based on experience with consulting jobs developing web applications using several Java frameworks, Ruby on Rails, and Portable AllegroServe with WebActions (open source Common Lisp frameworks), I believe that choice of framework is less important than:
  • Programming language: choose a language that both fits the application domain and has good library support for your application
  • Data modeling: while I believe in interactive bottom up development, spending time up front getting object models 'right' makes development easier
  • Object persistence: there are lots of good choices (prevalence, object relational mapping for relational databases, distributed memory only, etc.) but choose a scheme that makes sense both for development and deployment
I think that these 3 issues are all more important than choosing a web UI framework.

I have been investing a fair amount of time learning Erlang this year and the ErlyWeb framework (that uses the high performance Yaws Erlang web server) looks very good for both interactive development and distributed deployment. For web applications that map well to Erlang, ErlyWeb allows Erlang to be the development language of choice, but again the important choice is programming language selection rather than web framework.