This is how Quake Live works too - after a small download you enter a 10 minute warmup/skill-determining match against a bot, the rest of the maps carry on downloading while you play. In my case everything had finished downloading by the time I got out of the warmup.
Part of me really wants digital distribution of games, especially if it means cheaper titles. On the other hand, I'll miss being able to sell games to save money on new ones.