There's not much more that we can add to this, other than the thought that, even as we speak, SOMEONE at the House of Jobs is doing an impersonation of Dr. Evil, pinkie to the mouth and all, crowing "Half a BEEEELLION downloads! Mwuhahahahaha!!!"
Seriously, it was a mere six weeks ago that Apple bragged of 10,000 apps and 300 million downloads. This, folks, is the textbook definition of "exponential growth." The Palms and Blackberries and Androids and WinMobiles of the world have a hell of a lot of catching up to do.