I went with Steam, so theoretically you pre-load the game two or three days before the release, but it sits encrypted on your hard drive.
Then at release they send out the magical signal that begins the decryption, after half an hour you're good to go.
BUT
I've done this before and had less than satisfactory results. Sometimes they get swamped or there is a glitch and the game doesn't decrypt within the first day or so of release.
I got burned staying up to midnight in this manner on L4D2 and BF:BC2. Don't know what the problem was with L4D2 but with BC2 I'm pretty sure it was EA dragging their heels on a fix (since EA was also selling copies on their crappy proprietary digital distribution service).
So, if you're going Steam, give yourself a good night's sleep and get an early start in the morning rather than staying up waiting for it to decrypt.
svcks for me, I get high school right in the morning. Earilest I can play is 3PM.
On the bright side, the load on the server should have died down by then.
I recently pre-ordered Portal 2 and experieced first-hand and how pain-stakingly slow Steam's decrypting process is..