In under 9 months the app store has grown from 0 to over 30,000 apps. To break that down a little, here are some stats from our old 10,000 Apps page -- the image isn't up to date, but the stats are updated every few minutes:
Number of apps (some currently inactive): 30,005
Number of games / entertainment apps: 10,126 (33.7% of total)
Number of apps submitted in September, 2008: 2,944 (98/day)
Number of apps submitted in February, 2009: 5,872 (209/day)
Number of free apps / games in the store: 7,086
Total cost to buy every app ever submitted to the app store: $81,444.81 ($2.71 average/app)
The app store will be 1 year old on 7/11/2009 -- if things continue on this growth curve, we should hit 50,000 apps by then. That feat, for a new platform and distribution model, would be amazing.
Note: Philip Elmer-DeWitt Apple 2.0 blog on Fortune.com has some more info and some interesting analysis. He believes the tide of new apps has slowed. February, 2009 was the largest month ever, and it's still early in March -- we'll have to see how the month finishes out before we'd agree with that theory.