YouTube++ is a Chrome Extension available from the Chrome Webstore.
While I tend to think of it more as a mashup than an actual YouTube video edit, after I got over some of my initial "user confusion" I thought it was a pretty cool extension.
What confused me was when you began the extension the video was already spliced in quarters. I was confused on if I should be in the movie camera interface or the pizza. Overtime, I realized the spliced videos in the movie camera interface were post edit. One uses the pizza to mashup, edit, splice, and save the segments and the movie camera to interact with them. It was not clear to me initially that the piece of pizza was edit mode.
In the edit mode - Pizza - you can splice the video at exact time points and then name the splice and time. After you are finsished with a splice you can save it. You can continue creating as many splices as you want following the same steps.
In the viewing mode - Movie Camera - you have your spliced segments that you can interact with. You can even move the splices around if you want. Each splice allows you to play or loop the splice. I like that I could have a segment set up to loop again and again.
I think YouTube++ could be a valuable tool for educaters. Maybe you want to engage "youth culture" with a Justin Beiber or Miley Cyrus video, but only the school friendly segments. Or maybe you are examing a longer video and you'd like to just highlight a few clips.
Either case give the extension a try.