So after reading your post I decided to do some sleuthing on my own website, as well as some general You Tube searching and here is what I found...
Although I can definitely go back to February and look at the ISPs of people who visited my site, there are approximately 200 from that same 48 hour period (12th-14th). While 200 ISPs isn't that many to sort through (comparatively, anyway) it's still a hefty number. Along with the ISPs, it also gives me a town name. Now, this isn't that helpful since sometimes the registered town isn't anywhere near where the actual person and computer were at the time. My own ISP shows up as "St. John's Island, SC" and I am several states away from that. I had my neighbor get on HIS computer in his house and visit my website today. Although we are approximately half a mile apart, our ISPs are the same. Plus, in the three times I visited my own website and in the three times he visited, it registered several different ISP numbers so there wasn't even consistency in THAT.
As far as You Tube videos go, the information I gathered says that ISP addresses are only registered when the person comments, not when they view.
My conclusion, and this is strictly my own opinion from the little experiment I did on my own site, is that while this information might be good when putting a case together to tie it all in, I am not finding it generally useful to narrowing it down to one person. If they had a suspect and were looking for motive and opportunity, they might be able to look up his ISP address and track it to see what sites he visited but to do the reverse is a lot more complicated. A good defense attorney might even argue that it wasn't the perp's computer at all. They would need access to his own computer and his history to really make it "stick."
All of this is moot if the suspect did any commenting.