I always use the name robobunny when it's available. It is often taken already, which I guess is understandable. The thing that really annoys me is when the username robobunny.com or even www.robobunny.com is taken. Why would anyone other than me want to register my domain name as their username? It boggles the mind. If you are going to pretend that you have a website, you should at least pick a website that is popular.