I think robertlee makes some good points. A low ranking black belt (1st dan, some even have "zero" dan) symbolizes mastery of the basics. Beyond that you could argue the dans/degrees are steps toward becoming a master. For a lot of styles that is 5th dan.
IMHO what black belt REALLY SHOULD represent is someone who can dish it out and who can take it. It's unfortunate that rank is such a joke at soooo many schools. If you want to really BE a black belt, you damn well better have tested yourself.
I got 2nd dan in one style, but I didn't want to go on because I didn't think going onto 3rd would really improve me. Plus, there's always politics and the almighty dollar along with it. Now I'm basically one of those "masterless samurai's".