1) Change Thumbs up to Thumbs Down
2) Change Thumbs down to Thumbs up
3) Remove thumbs up
4) Remove thumbs down
5) See a list of your thumbs up for a playlist
All of these should exist, if not in the app at least on the website.
Updated on 2019-05-23
It seems like this idea has evolved into a lot of different threads over the years. Quite a lot of the features requested do exist, so I'm going to mark this as implemented - but if you feel like your specific idea isn't there please feel free to make a new idea.
As a heads up, Thumbs up/down has been replaced by the Heart/Remove symbol across all platforms. Let's address some of the main ideas that have been implemented:
I hope this clears some things up.