I'm a long-time macports user, and brew just blew me away with how much less work it made me do! (even just in terms of other source builds finding libraries by themselves - a real boon.)
I'd really like to use both macports and homebrew, and switch between them as necessary, but I don't know a good way of doing this. I know homebrew is relatively well-behaved and doesn't really put stuff outside /usr/local, but other things install into /usr/local too so I can't just remove that from my PATH when I want to use macports.
If anyone knows a reliable and simple way to do this I'd be very grateful.
I'm not sure to what extent this works with brew, but you could try using virtualenv to manage different environments?
I've never had to deal with multiple configurations on the same mac (my solution, off hand, would be to use debian VMs, possibly through SSH rather than a desktop GUI if I needed >1 at a time.)
If anyone knows a reliable and simple way to do this I'd be very grateful.