According to AndroLib, the Market has over 100,000 apps. Unfortunately, Google disputes this in their earnings call, saying there are about 70,000 apps. Regardless, this is up from 30,000 in April. I would still say that it is quite impressive growth. To put this in perspective, it took from October 2008 until April of this year (about a year and a half) to hit 30,000 apps in the market. Yet, in three months (!) it more than doubled. Seems that Android is catching on.
While the number of apps in the market might be off a bit, AndroLib has some other interesting data. Over a billion apps have been downloaded (although it is unclear whether they are talking about upgrades as well). Over 15,000 apps came out in June alone, while over 11,000 have come out so far in July. You can check out their stats here.
I imagine that this growth curve will have even steeper acceleration with the advent of Google App Inventer. I know I am waiting with bated breath for Android to surpass the iPhone in anything, and the number of available apps is a great indicator. What do you think?