Must say im impressed with its steam implementation.
It asks me to install some useless gamespy chaff on every load, and keeps looping at the CD Key screen. Spot on.
Ace, Rumors are its caused by SecureROM, which has been affected by the PSN outage.
http://forums.steampowered.com/forums/showthread.php?t=1875468&page=9
Thanks for that, figured I wasn't the only one!