Following the normal trend, I basically never register for anything unless there's a particularly good reason.
Unfortunately, my patience is usually low, and if registration takes me longer than a minute or two, or if when I register I get redirected somewhere that isn't where I was trying to go, I often lose interest. This happened just today, in fact.
I'm annoyed that I have something like 65 account login/password pairs to keep track of now. Most of them are the same, and really I've only got about 6 variant passwords and 6 logins, so there's only really 36 possible combinations to try for any given site. Still too much though.