That's pretty neat. I wish that it had a little more language support though. As a recreational activity, it'd be nice to be able use something a little more modern than Java.
I have been pondering the possibility to build a challenge problem site that accepts solutions composed in languages other than c/c++/java/c# . Interview street has done some for languages from Haskell to scala to php. But probably I will include javascript because javascript is going to be influential on html5 apps.
If anyone has similar idea and like to team up. Please contact me.
That would be really cool. Another thing about doing it in JS: you could then potentially use something like emscripten to automatically support other languages.
spoj.pl is very similar to acm.uva.es, but also has a much wider array of supported languages.