Justin Gehtland has opened himself up to some critique after boldly coming out with some performance numbers wrt an application that he ported from Java to Rails.
There are definitely areas in which you could jump on the numbers, but I would rather not try to make this a “which is faster: Java or Rails”, but consider that, as he says… Rails can perform fine.
One of the big points though is the fact that there IS a large difference between performance and scalability.
Also, the tests that Justin has had time to do are only a small slice. It would be great if we had resources to do some serious performance work. Maybe like the PetStore? ;)
Brian Mc has some great thoughts in Expressiveness Matters. It is particularly interesting to hear him talk about caching in the platforms, and his C/ocml story :)
NOTE: Brian also is your friend if you are a Lucene user, thanks to his Lucene/Spring integration