Adobe InMarket <http://phtshp.us/c0qox4> includes this kind of info if you
want to distribute a paid app. I believe the AIR marketplace also offers
some data but I believe it's very limited.
Another option which I really like is App Analytics <http://bit.ly/9SCmMK>.
You can use that or something like Google Analytics if you're going to
handle your own distribution...
P E A C E
You could also embed code into your application that runs on first install.
Say the code checks for a text file in ApplicationStorageDirectory. If the file is not found, it makes a remote call to your server, then adds the file so that future checks fail.