Sorry so late on this, I'm only on every few days We did a registry at jillian's drawers, and just like what everyone else pretty much said, we bought our own prefolds off GMD because they were the cheapest, and registered for the covers and nicer dipes and accessories (wet bags, wipes, slings, detergent). One of our friends had already planned on hosting a "diaper shower" for us, which was just for our closer friends (was co-ed, turned out to be a lot of fun), so we knew doing the registry would be worth it. Not sure if you guys would be able to do that or not, but it was definitely awesome.
Diaper-wise, we ended up getting most of our KL's, all of our covers, and some of the AIOs (BG,thirsties,FB). Like Lauren said, the selection is awesome, so you can really choose what you want. The only annoyance (and it was minor)...when they have good sales on certain dipes, some of them will sell out quickly, so you have to keep a close eye on the registry to keep it updated. Two of our friends had trouble buying a certain dipe that was sold out (but it didn't say that when they went to purchase it). All in all, we were very happy with how everything worked out with them. Good luck, hope this helps!