I'm not a Linux graybeard by any means. I installed Ubuntu back on July 4, and I can honestly say that I haven't booted into Windows in almost two weeks. I haven't needed or wanted to. (I spend most of my time playing with the LAMP stack.)
YouTube works fine, as does every other Flash site I visit. I had an issue the first time, did a GIS for a solution, did whatever it said, and I've been fine ever since. No browser crashes or anything, and this is 64 bit Linux. Was it as easy as it is in Windows? No. But it wasn't terribly hard, either.