As with all crowdsourced software, StumbleUpon's not terribly good at its job right off the bat and a moderately unresponsive UI (with tiny touchscreen buttons) doesn't really help, but the app presently pulls from a set of existing Android app databases that give it a nice head start. After you log in with your StumbleUpon ID, it asks you if it can (a la AppBrain) take a look at the existing apps on your phone, after which point it displays likely correlations one by one (complete with descriptions, screenshots and Android Market star ratings) for you to vote up or down. We got quite a few flashlights, soundboards and fart machines, mind you, but most everything we saw had plenty of ratings and at least four stars, and a good number of our favorites (and some probable soon-to-be-favorites) popped up as well, and voting up and down app concepts is an amusing diversion in and of itself. Sadly, it doesn't use your existing StumbleUpon topic preferences to recommend apps, but it will hopefully align them to your tastes soon, assuming that enough folks can look past the iffy UI long enough to help their fellows and give the free app a go. PR after the break.
Update: It's on the Android Market right now -- find it at our source link, or use the handy-dandy QR code at right.