For those waiting for it in stores, I think tomorrow is more realistic. Today is the SHIPPING date, so they usually ship from their warehouses today to reach their stores or direct order customers the following day.
I am sure there will be some sightings in some stores today, but the vast majority of retailers will be receiving their stock tomorrow. (I have no inside information on Gal Civ II, but having worked years in a Big Box retailer, as well as being a rabid commuter gaming fan, experience does teach me a few things. )
You also have to allow for yesterday being a Holiday, shipping times, the time of day shipments arrive in stores, and the speed store personal can check shipments in and stock it on shelves. You might want to call ahead before driving any great distance.
Stores like EB, that specialize in games, will get it out pretty quickly. Big box stores such as Walmart and Circuit City may not be as excited about getting it onto the shelves as we are.
Those of us that ordered the DL also have to allow for possible problems getting the final download with net and server capacity being finite. A recent DL add-on for Flight Simulator crashed the download servers of the distributor despite this being the fourth or fifth release by the developer. It also crashed the forums of the largest Flight Sim support site because of all the buzz and anticipation. Stardock has done everything they can to be ready, but things can still happen.
Patience, everyone. We will all be playing soon enough.