My experience with OS X was that I had official installations, Homebrew installations, and some thing else on top of that that was purple or a bird or something (Pidgin comes to mind, but it's obviously not that) and none of them played nice with each other, and none of them provided all the third party modules I wanted. Part of why I ditched OS X for Linux, in spite of Spotlight and the multi-touch keyboard, both of which I really miss, was that nothing played nice with each other. Different Python installs only worked with their own locally installed third party modules. It wasn't a feature, like virtualenv, it was just a limitation.
That said, it was about three years ago that I had that experience. Perhaps things have progressed since then. But I would definitely recommend using one thing and sticking to it, and pip and virtualenv both work on Linux too, and I'm a fan of using multi-platform tools where possible instead of something like Homebrew which is Mac specific.
As for actual experience... before I learned about virtualenv, which as you noticed is super awesome, I had everything installed alongside everything else, and everything used the same most recent (Python 2.7.x) version. I luckily never came across any versioning issues. If I was given a production machine for a new project, I would certainly use virtualenv instead of just installing everything to a central site-packages directory, because even though you might get away with it, when you don't really bites you in the ass. (Some co-workers of mine had a project which required a particular version of pygame, and a particular version of sqlalchemy or something of the like, and had issues that were resolved once they used virtualenv properly. Keeping all installs through pip also helped, IIRC.)
Also, anything of importance I've seen deployed has always been in Linux. That doesn't mean that you shouldn't use OS X, it just means that my recommendation for using the standard Linux tools should work on OS X but if it doesn't, then I don't know what to say.
Join the #python-forum IRC channel on irc.freenode.net!
Please do not PM members regarding questions which are meant to be discussed publicly. The point of the forum is so that others can benefit from it. We don't want to help you over PMs or emails.