Empire: Total War is shipping to stores in Europe and North America today, but if you do get a copy, you may have trouble authenticating thanks to a ridiculous staggered release, all centred around Steam's exclusivity deals:

Tuesday, March 3rd - 1800 CET / 1700 GMT / 0900 PST

North American & Canadian Ship Date
Steam Authentication Servers activated for North American & Canadian Retail customers.
Steam Authentication Servers activated for all European and other Worldwide retail and digital download customers.
Game available for sale and download for European and other Worldwide digital download customers.
Wednesday, March 4th - 1000 CET / 0900 CET / 0100 PST

Worldwide street date.
Game available for sale and download for North American & Canadian digital download customers.
Firm release date info only became clear today following repeated enquiries by Creative Assembly staff, who were unaware when their own game was digitally available. Additionally, Steam promised customers a pre-load, which will now no longer occur. Buyers are furious, primarily because the download is 15GB. Yes, you read that right, the compressed download is 15GB, making Empire: Total War one of the largest games ever released. Those with slow connections, who were unaware of the enormity of the game, will either have a very long wait to play, or will have to demand a Steam refund, something which Valve is typically reticent to do.