Just connect with your friends (using Facebook, Twitter, or your contact list) and you can then browse your friends apps. Zwapp detects apps automatically on your device with a few clever tricks.
Also the real-time feed shows you the apps your friends are downloading now, reviews, likes etc.
By Clever, do you mean a private API? I'd be interested in how if not!
we do two things:
1) We check on custom schemes (btw: watch that space as we will open source our work on that shortly!)
2) We check processes on iOS4 devices and match those as well.
The algorithm learns and will detect better and more with increased usage.