I have one, and I like it! Don't buy it from ThinkGeek, though, because their price is too high. I've seen these fridges sell for $55 each on EBay, AC Adapters included. A co-worker of mine also found one for $39 at a discount warehouse, but it didn't come with the $20 AC Adapter.
To answer your questions:
Yes, they work great! It's usually best to cool your sodas in a real fridge before putting them in the Cool-IT, because it takes about 6 hours to chill them, otherwise.
And, yes, they DO hold a six pack very well. They are too narrow to hold much of anything else, though. Forget about sticking those 20-ounce Coke bottles in there, they just won't fit right.