I just got 2 AWUS036H's in the mail today and can only say they are amazing. I had previously been using the BCM4312 that is built into my portable and after reading this I decided to test it out myself.
From a range of 5-10 meters from my own AP, I am seeing at least 3x the packets and beacons from the alfa than my broadcom. I am using the packaged 5db antenna and the house is constructed of solid concrete.
Attaching the 9db (also came with it) I don't see much change, but notice a slightly better connection (no more than 5-7 db).
Wondering if maybe you got bunk adapters I decided to try my other one, but the results were the same. I also had a friend setup an AP in his window and I was able to hit it from about 400 meters with the alfa, but the broadcom couldn't even pick it up. I suppose its still possible that you got a bad "card", or something between the signal and your PC isn't working properly.