Having 'me' as a user entity would be useful:

• it's sometimes less characters to type than your own name, and lookahead/reoslve could be instantaneous for it, as you don't have to wait for server typeahead (although you can technically cheat and just always have your full name preloaded and bound to the first letter of your name)
• It's useful for custom query construction (resolve 'me' on query execution, instead of query save)

And yes, I'm aware that 'me' is already taken on this Phabricator :)