Why does my computer itself show up on Shared in Finder?
I've seen this happen after a restart - I believe it is to do with Bonjour and has something to do with Bonjour not releasing the name during the shutdown process. When the computer restarts and tries to register with the same name - it appends the (2) / (3) in order to preserve unique names.

There might be a few things that do not work for you after this - for example, other users on your network who have bookmarked or otherwise stored links to your Bonjour services via your original name won't be able to connect properly. I've also seen issues with Mail and a few other Apple apps after the name change.