I'm a little confused by the competition dance categories, i.e. Silver I, Silver II, full Silver, closed, open...does anyone know what the difference is?

Beside age categories, USABDA only has 6. There are 3 syllabus, plus the newcomer: bronze, silver, gold. As you go up, you're allowed to do more steps because you've proven that your level of technique's sufficient. The open categories are novice, prechamp, and champ. They have no syllabus, but they get harder as the level increases.

All the NDCA levels are put in place mainly so that the pros can dance with more students and so that the students can feel like they're really progressing when they go from Bronze I to Bronze II and so that more people get pretty little ribbons. Sorry-- I went to an NDCA comp once (I competed Am/Am). I hated it. It was a joke, because almost everyone won. I'm used to going up against 60 couples in my division. When I win first, I really feel like I've accomplished something. Somehow, first against two other people seems like a waste of time.