Time for a helpful public service announcement: if you've pre-loaded a copy of Modern Warfare 2 on Steam, you won't be able to play it later tonight like everyone else.
Yes, while anyone buying a boxed copy of Modern Warfare 2 on PC had only to wait until November 10 (i.e. now) to play the game they already own, if you've pre-purchased the game over Valve's Steam service, you have to wait a little longer.
Despite both games employing Steam as a means of DRM — hence the lockout — Valve confirmed with Kotaku today that customers purchasing a copy of the game over the same system allowing retail buyers to play on the 10th have to wait an extra two days until Thursday, November 12. In Valve's own words:
Those who purchase the retail copy will be able to activate and play the game on November 10 via Steam.
Those who purchase on Steam will be able to activate and play on November 12.
We asked "uh, why?" and have yet to hear back from Valve, though we suspect it may have something to do with avoiding the rush. We'll update if we hear anything more.