Valve has provided some decent motivation to do so quickly, if fun isn't enough: if you play on a Mac before June 14, you'll get some in-game earbuds like the ones sported by the blue "Mac" team in the above video. Oh, and you can also play for free this weekend (through June 13) on both Mac and PC, or pick up a permanent copy of the game for $10. Both of those offers are good through June 13.
[Thanks to all the excited Mac owners who sent this in mid-freakout]
