For work and other reasons, I've been spending more and more time recently on Linux. I saw one of my colleagues using a "Powerline" - style bash prompt, looked into it, but when I discovered it invoked Python every time you pressed ENTER and failed abysmally on my "does it run OK on an 80MHz MkLinux PowerPC 8100" test (don't ask), I decided to write my own version in C, not bothering with a lot of stuff I didn't use, but still allowing themes. This is tpwl.
Anyone interested in a Powerline-style bash prompt on their Macs (warning: C compiling required) feel free to have a look here (github.com).
It was written on Linux but works fine in Terminal on MacOSX. For best results install the patched Powerline fonts (I use Anonymice).