Yeah, to celebrate the launch of the Pyro update, Valve have announced that you'll be able to play Team Fortress 2 for free this weekend, you'll just need to pre-load the game and you will be able to play it.
Anyways, this is ultra good news for me, as I only became interested in the game yesterday, after playing it (360 version) over a mate's. Really, really good fun. It's also good news because I finished my last exam today, which means (aside from next week's prom) I will never go to that school again!