I do sort of both by running Debian inside Virtualbox on my Macbook as a dev environment. I especially like being able to install -dev packages to get header files/libraries into the right places, whereas on OSX, if you want to compile software that depends on anything that didn't come with XCode, it's a mess of manually extracting things and passing pathnames.

I don't go the whole way and just install Debian on the machine mostly because having OSX handle things like the touchpad driver, hibernation, wifi, etc., is less hassle, and I also like OSX as a desktop environment (e.g. being able to use multitouch gestures in the browser). But Linux in a VM is definitely a nicer experience imo than fink was, as a way of getting a parallel Unix CLI userland onto OSX.