I just checked the tag cheatsheet and this site doesn't have a way to exclude posts that one has already favorited (or to search for a specific tag within your favorites). It would really help if when a person looks up and artist that he or she likes, he or she can make it so they only see the works that they haven't favorited yet.

Also maybe a similar feature for posts one has liked or disliked.

If you try and favorite an image that is already in your favorites, the board will not add it, but tell you it's already there. So you really wouldn't be doing much other than saving a few seconds.