In December 2009 alone more than 280 million apps were downloaded generating over $250 million in revenue. There are now over 58 million App Store users, each spending over $4 per month, as this Gigaom article reveals (excellent article with a really neat graphic full of stats, check it out).
Interestingly, this huge growth in December can be partly explained by, you guessed it, the Christmas Day download figures, which caused a spike in downloads on iPod Touch devices (looks like a bunch of lucky people got iPods for Christmas!).
Because of this, downloads in December increased by 50% over November. It will be interesting to see if January holds up to this growth, levels out, or drops due to everyone getting the initial apps they wanted out of the way.
(Graph source Flurry Analytics)