yeah, thats what I do!!!
What they say:
This site is a quick and dirty solution to a question that I often lay awake at night worrying about. Do I have my username registered across every site that I should? What if the next internet humiliation meme just happens to share the username I’ve been using for years, and suddenly people are emailing me asking “hey, is this you ???”
UserNameCheck lets you check if the username of your choice is available or taken on a host of different sites. At the time of writing this post, I was able to check for username availability for 68 sites!

Go ahead and check if your favourite username is still available.
kiran
November 17th, 2008 at 10:36 am
i am checking mine. would you register on each and every website and grab your username?
Nischal Shetty
November 17th, 2008 at 10:48 am
@Kiran
It depends on the website. If its good enough and interesting then I would register