Okay, I'll be fair. Mono isn't that bad. Unfortunately, the emphasis is on the that. However much it would be nice to port .NET applications to any *nix variant (including OS X), Mono doesn't work nearly as well as the .NET framework on windows does.
On topic:
Actually, I also recommend learning at least a little bit of Lisp (or a Lisp variant, like Scheme, if you prefer angle brackets over parentheses). Lisp, I daresay, is one amazing language.