- the browser isn't integrated with my keyboard's Play / Stop buttons and my apple remote
- YouTube history sucks, as it gets wiped every session
- I want to watch all those
illegal music videoswonderful user-generated movies offline

It does concurrent downloads, and tags the unseen videos. This is convenient because I can get multiple variants of the same video, and see / delete the bad dupes. Unfortunately, it doesn't meet my main request -- no integration with the keyboard or apple remote.
Hope this helps people looking for something similar! Please comment if you find something better.
Happy watching,
Victor