From the YouTube blog we get the following
Years ago we created a way to link to a certain moment on a video, which let you find, share and comment on just your favorite parts. Now we’re expanding that control even more. Over the coming weeks, you’ll be able to see an image preview or a series of thumbnails with three new features on our video player. So whether you’re sneaking a peek ahead, scanning backwards, or using a thumbnail to find where you stopped watching a video, you’ll soon have three options to instantly look through YouTube videos.
Here are some screenshots of the new features
Long video zoom in
Of course, the downside is that this will not be available on all videos immediately. As noted in the blog post there is an hour of video uploaded to YouTube every second (yikes) so this may take a while to be on every video.
Until that time though I have to say that these features can make the video viewing experience very different and that is a good thing.