It seems YouTube has enable the use of hash tags in comments.
While the YouTube blog has yet to mention anything about this, it seems that the most frequent hashtags get an orange framing, while the rest are just ordinary links. (It’s a bit funny that what is probably the most used comment on YouTube, «GAY!», did not get an orange frame. Those poor trolls.)
I also tested it on a channel site, but seems that the hashtags only work in video comments.
This seems like an exciting and useful addition to YouTube. The most used phrases like lol, omg etc, are probably not worth tracking, but if you have more specific #hashtags you’ll be able to follow discussions across several videos.