Team Fortress 2, a free to play first-person shooter (FPS) multiplayer game, is now available for everyone using the Linux Steam client, and not just those who have received a beta invitation, so non-beta users shouldn't see the "server is too busy" error when trying to download the game any more.
It seems this is a mistake from Valve, which fixed a bug that prevented Ubuntu Developer Summit participants from playing Team Fortress 2 and in the process, somehow the game ended up as being available for everyone. This might mean that Team Fortress 2 won't be available after Valve fixes the glitch, but considering they haven't fixed the bug that allows non-beta accounts to use Steam for Linux, they might allow this as well.
To play Team Fortress 2 in Linux without a Steam for Linux beta account, firstly install Steam for Linux, then launch Steam, search for Team Fortress 2, click the "Play game" button and then wait for the download to complete - it will take a while since 12 GB of data needs to be downloaded.
Tip for those who have TF2 installed on Windows: you can copy the .gcf files from the Windows installation to ~/Steam/SteamApps/ and rename each word to start with a capital letter (e.g.: "Team Fortress 2 Client Content.gcf") to speed things up - only a few MB of data will need to be downloaded once you do this.
Note: in my test, the Team Fortress 2 download seemed stuck at 99%, but I was able to launch the game anyway and although it took a while to launch it for the first time, it worked just fine. After that, the Steam for Linux client displays the game as being installed successfully.
Oh, and remember that Steam is currently in beta, so things might break, you might get bad performance or the game might not work at all for you.