>>>Ruby on Rails is good. It not only gives you bang for your buck but bang for your time (both learning and developing), which may be more important.
>>
>>except performance, from what i hear
>
>I don't know, Twitter is created with Ruby on Rails. http://rubyonrails.org/applications

This may be old but:
http://techcrunch.com/2008/05/01/twitter-said-to-be-abandoning-ruby-on-rails/