There are tons of social networking sites, but with that there are several users who use the same username you want to signup with the service. The problem is pretty much a everyday issue for many users.
So just as you are about to signup for a social networking service, you see a error message telling you that the username you are trying to signup for has already been taken.
So what can you do about it? Practically nothing, but you can at-least save yourself by using Username Check to see, which social networking site is available to signup with your favorite username.
To check if your favorite username is available, go to http://usernamecheck.com and enter the username, once you provide the username, the service will check the most popular social networking sites and tell you whether a username is available or not, it also provides you with a link to quickly signup for the service, if the username has not been taken.
So go ahead and see which services you can still sign up for with your favorite username.