The newest official blog post seems to indicate that. The post indicates that there will be a big announcement tomorrow for the game, and several clues point to the Mac version of TF2. Such clues include the white earbuds being sported by the TF2 characters along with the note that the announcement rhymes with "Speem Gortress zmavailable on the Babac." TF2 will join the Half-Life series as those Source games ported to the Mac. If the Half-Life release was any indication, we should be able to expect a sale on TF2.