The Ruby on Rails Web application development framework (
http://www.rubyonrails.com/ ) looks really great. I have always liked the look of the ruby language, but never had reason to learn it (I already use too many!).
But as quoted on the homepage, "Rails may be the project to take Ruby mainstream".
From my cursory investigation, Rails looks like it would be very time effective from a developers point of view. I've also never regretted following Lars' lead on software (vis. emacs ;)
I'll let you know when I have a sample app done, but that will eb a while yet - Perl/mason and OpenACS are still filling my head :)