I don't think I really recall having any username regrets. The only usernames that I've used over my time online (that I can recall anyway) are: threeisacharm, knowlee_raven_2007, knowleeraven, knowlee, knowlee_raven, and knowlee_goddess. (yeah, a lot of 'knowlees' in there. XD)
The only two that I've used that are actually dead now are threeisacharm and knowlee_goddess. The first one was for a quiz-like forum that I never go to now simply because of the fact that it's a different type of website now and the second one is from a now deleted FreeWebs account that I made to promote a story that I used to have. Other than that I use the username 'knowlee' or a variation of it at nearly every website I make an account for. I don't regret using that username, I find it to be quite unique (even though I've discovered that there are other people who use it as well on other places.
) and I love how it is spelled and how I pronounce it.