Apparently, Saints Row: The Third is getting a free weekend of play on Steam. The trouble is that it's kind of hard to find out how to start pre-loading today as per the advertised instructions. Thankfully there appears to be a solution on the official Steam forums.
As posted by Whisperity, the pre-load subscription should already appear on your Steam accounts as "Saints Row: The Third Free Weekend - Sep 2012 (Complimentary)." You should see it in your purchase history but not in your game library. So it looks like someone just got a little too excited and set this promotion live a little early. Expect this to be a more fully functional pre-load at some point tomorrow or Thursday, giving you plenty of time to get Saints Row: The Third ready for play this weekend.