Doom 3 came out today, and was immediately purchased by everyone who hadn't already downloaded it from one of the myriad Bittorrent feeds that had it available all weekend. I checked last night, and there were about 5000 people at once downloading the game (a 1.7 gig file, I think) just in the one place I was looking.
It's different, but not that different from a decade ago. I co-wrote a book last year looking at the history of video games, and we started one chapter talking about the huge traffic jam of people in 1993 waiting to download the original Doom from FTP servers. The guys from id Software couldn't even get onto the servers to put the shareware game up.