A control freak will cut you off from your friends so you do not have an escape.

A dominant will allow you to bring your friends around because he wants to knw as much about you as possible.
I'd like to add that a dominant will also not discourage you to have friends and contacts outside the relationship -- control freaks have a very strong tendency to do exactly that.

Also, they are not necessarily open with it -- they don't usually say "Hey you, you are no longer allowed to see your friends" but they will make you feel guilty or weird about it. Or, if that fails and you still go they will start to badmouth your friends, insist that they have a bad influence on you, are worthless, mean, only exploiting you...and generally wear you down until you think it's easier to simply stay at home -- which, if you are very lucky, will get you the reputation of a recluse who is no fun and always stays at home instead of going out. Yes, control freaks are fun. Excuse my while I get a drink to get rid of the bitter taste in my mouth.

Another difference that just occured to me, at least judging from my perception:

Control freaks tend to be highly possessive and jelous. Dominants appear to be much more secure of what they have.