I believe that most modern MMOG servers are built primarily in C/C++, with Python/Perl/Lua/whathaveyou used for scripting various parts.

Owing to the amount of data these things have to handle, and quickly, I've a feeling that networking, object management, physics and the like are best done in C/C++ or the like.

As for Python over Perl, I've been told (but have no personal experience in this, mind), that Python has a cleaner embedding interface than Perl.

Personally, I'd prefer to use Parrot for this sort of project - best of all worlds. However, there's the slight limitation that it's not done yet...