Tubetrail does not depend solely on Active Sharing to figure out what you're watching. Instead you have to install a small browser extension (currently Firefox only) which keeps an eye on your viewing habits. Videos you've watched are then presented as embeds on a large, colorful grid where your friends can go and watch what you've been viewing in reverse chronological order.
As an added benefit, you can add a special comment that will only show up on your Tubetrail page, and not as a user comment on the YouTube video page. These show up underneath the videos, and are denoted with a large exclamation point on the grid.
The service has two weaknesses, which I think if addressed would make it more compelling than YouTube's offering. One of those would be to create an RSS feed out of items you've watched, which would let others view your picks, and see your comments from someplace other than your Tubetrail page. Second, if I'm going to install an extension that provides little utility outside of YouTube's built-in sharing tool, have it work on YouTube videos that are embedded off YouTube's site--something which is not currently offered.