
With 47 million views on Youtube the above video posted by "guitar90" is an astounding web phenomenon.
There is some interesting Integration Marketing happening here, but fist let's take a look at the back story.
According to the New York Times, the actual person in the video is not "guitar90" but "funtwo" (Korean guitar virtuoso Jeong-Hyun Lim).
If you read the info section for the video it is written in the first person and one would get the impression that it is the voice of the guitarist himself. No one knows who guitar90 actually is, though ...
And here's where the genius Integration Marketing comes in - there is a plug there for a guitar training system and an implied endorsement.
Now, I'll refrain from comment on the ethics of snagging someone else's video and implying that you are the author. I only want to marvel at the brilliance of the Integration Marketing example.
What you have here is an enormous Traffic Stream (the Youtube video itself) and a well-placed UMV (Unit of Marketing Value - in this case the endorsement of a guitar training course with a built in response-mechanism: the link).
I wouldn't recommend snagging someone else's video to do this. Of course claiming the video as your own and then using it in advertising is just, well, completely uncool. (I could be wrong here - maybe funtwo is getting cut in on the action - I sure hope so.)
Either way, you get the point: Create a viral phenomenon and then integrate your UMV at the appropriate Integration Point. Note that I doubt this would have been anywhere near as effective if it were in the format of an infomercial. If they had integrated their UMV inside the video itself it would have seemed disingenuous.

There's quite a few people who recommend downloading Youtube videos, "rebranding" them and uploading them under your name.
Their reasoning. "Hey, these people are amateurs who just want to be famous so they're happy for ANY views they can get."
Much better if you see a good viral video on Youtube to contact the owner and suggest a JV. All legal and above board.
Martin