I'm not exactly sure what you mean when you say, "search for tags that other have used." However, there is a way to "discover" what tags others have used before you.
When you are tagging an item, and you begin typing a tag, if there are other tags that anyone else has used before that begins with same letter(s) as you type, those tags show up in a list that gets filtered as you type. This is the only way I know of to discover other tags. If you wanted to find out who was following a particular tag or see other information related to the tag then it appears you would have to tag something with that tag before it would show up in your My Site.
