Generally speaking Youtube is possibly one of the worst places ever for feedback/reactions to almost anything unless it's universally awesome, like that Mythbusters where they used a rocket to slam a thick plate of metal into a car at nearly the speed of sound. Most of it consists of pointless statements that mean the same thing, a staggering amount of cognitive dissonance (especially on politcal videos), plus grammar and spelling that almost makes me want to cry when I think about the fact that it was probably written by an American (sometimes I wonder how a foreigner with a loose grasp of the language can derive the correct meaning from them).
Buried within all that there might be some comments that are genuinely worth something, but usually it's like trawling through the cesspool that is 4chan's /b/.
I don't watch youtube, perhaps because this reason gave me a terrible impression of it.
However, apparently, youtube on the Japanese side is more often used by people who are 20 years or older in age, while nicovideo is treated like the dumpster for mid-high schoolers, which surprised me very much indeed. I mean, just comparing comments between American youtube and Japanese nicovideo shows a rather large difference between the quality of commentators. As far as I've seen on the foreigner reaction videos on nicovideo, Japanese people don't bother to pick up any of what would be considered unnecessary junk from any country.
I guess comparing Japanese nicovideo to Japanese youtube, the quality of comments are better on youtube, just from looking at a few videos right now. This leaves me with the impression that only Americans have this problem on youtube.
Like you said, unless it's universally awesome, it's a terrible place for feedback. In other words, if it's just awesome within the American realm, it's a terrible place for feedback. Japanese people don't really need feedback on American things, just on Japanese things that become universally awesome to the point where there naturally would be foreign feedback.
From ones that come quickly to mind, there have been videos on vocaloids in general, touhou in general, Bad Apple PV, the CNN incident, and the Korea cyberattacking 2ch incident. I'm sure there'll be one on the PS3 calendar bug soon enough. Note also that America is simply a nation within these foreigner reaction videos. American feedback doesn't really come out more than the other countries that do.