Another feature, that might be trickier to implement: like in web browsers, pressing middle button could present a little gizmo that helps scrolling faster (I though about it for five minutes and can't think of a better way to describe that thing).
Well, I'm almost always on my Mac and use the trackpad, so I always feel a little awkward holding a mouse in my hand. But even so, I think if you have a large enough library (say 200 movies), it would take a lot to scroll to the end (I tried it right now: 40 seconds).
Unfortunately I haven't tested it on a Mac yet (I didn't know it could work, as the Windows GUI seemed native). I use Mac all the time, but my movies are on my old Windows PC.
I'll test it later on and see if there's any bugs :)
But shouldn't there be a button that lets you open the video you're viewing? Clicking and double-clicking don't do anything...