These have proved more difficult than expected, but we're getting close. We expect to also be testing Mac and Linux versions of QUAKE LIVE internally this month and then making those publicly available just as soon as we feel they are ready. This work is being done by a separate programmer in parallel with the other work that we're doing, and is his only priority - point being, that this is a top priority for us and not being delayed because of other work.
Personally, I want to know why support for Linux and Mac is even needed. After all, Quake Live is a browser-based game.
Anyways, beta is probably a good time for figuring this stuff out.