Miro is an application I first heard for at thepiratebay.org. It's a torrent client, a video player and a desktop portal solution for all media. It's free and integrates well with the pirate bay's torrent tracker. Unfortunately it doesn't integrate with local torrent trackers for some reason. Anyway it's very good for following youtube channels and watching cnet shows and most of all watching TED presentations.
It has versions for both Mac and Windows,
though I have only tried the Mac OS version, both look and behave the same. The GUI rocks, the player is light and runs nice.
The best thing is it downloads the youtube clips or ted presentations in HD and stores them locally. It's full of browsable free content.
One note: youtube channels have to be added with the URL in this format: http://gdata.youtube.com/feeds/api/users/hdstarcraft/uploads?alt=rss with hdstarcraft being the user name. Otherwise it complains for some reason.
Verdict: highly recommended.
Update (24.08.2011): Version 4.x (especially for Mac) is bloated with pointless features. It's not that fast and slim. It runs slowly. It crashes. And the most stupid thing I've seen - right/left arrow now goes to the next/previous feature respectively. To forward/rewind with 30 secs the Shift+right/left arrow must be used. So stupid. Cannot be configured.