I'm just starting to look at Ruby. It's the performance of Python that's driving my to look at other things. Code that runs on Perl (without much optimization), can take 5X longer in Python (with optimization). The whole immutable object thing makes Python spend all its time creating and destroying objects.
Python has always downplayed performance, but ultimately it limits how far it scales. You can create a hybrid system with C/C++, but that loses all the portability advantages.
Ruby appears to have performance closer to Perl, with the elegance of Python.