I really like Blizzard's solution : {$Username}#{$number} is very practical! It complicates thing a bit when you want to share your contact info to a friend, or

I really like Blizzard's solution : {$Username}#{$number} is very practical! It complicates thing a bit when you want to share your contact info to a friend, or when you try to remember a specific battletag, but it solves the uniqueness problem. And to be honest, on most sites I end up using numbers at the end of my username anyways, such as "Username0037".