Chrome: Comments on YouTube videos and Flickr photos are highly variable in quality, and finding the gems amongst the dross can be tricky. Chrome extension OpinionCloud summarises the comments so you can get a quick overall feeling.
The extension summarises commentary, pulling out the most common words from comments and presenting them in a tag cloud, which you can optionally split into positive and negative groups. As some commenters have noted, making that division isn't always easy, but it's still faster than reading through hundreds of often repetitious comments. We had trouble getting it to work with YouTube, but it worked well with Flickr.
If you still find YouTube comments distracting, you can use Comment Snob in Firefox to filter out the worst offenders.
OpinionCloud is free, works wherever Chrome does.