Since the game's engine runs on OpenGL, a Linux port is relatively easy. Whilst there had previously been suggestions that a Linux client might be included on the retail DVD, it seems that it will, in fact, be a downloadable client released shortly after.
Splash says that both Nvidia and ATI are keen to get the client out the door, which says good things about their level of Linux support, we think.
No word on when it may appear on Mac, however. Don't hold your breath for that one. ยต