From an interview with Bruce Tate, author of some O'Reilly Java books:
Siddalingaiah: Ruby on Rails is known for its rapid Web application development, but there others, such as PHP. The PHP community has developed mountains of opens source Web applications. Do you think PHP developers have something valuable to contribute?
Tate: Not really. PHP, and the ideas behind it, have been around for a while. It's quick and dirty. We know quick and dirty. Visual Basic. PHP. Perl. They don't excite me. Now, quick and clean, that excites me. Ruby on Rails is model-view-controller. It stretches the object-relational-mapping state of the art. It's quick and clean.
Well, I'm glad we cleared that up. You guys writing MVC apps with OO PHP5 and Perl can all go home now. (The idea that ActiveRecord somehow stretches the O/R mapping state of the art is pretty amusing too.)