But for me, gnash is still a no-go in a terms of processor power. And I wont buy a new quad core processor just to be able to play YouTube videos. Lightspark does a great job here, my good ol' Prescott 2.4 GHz handles very well flash videos and sites (performance is a lot better than with the Adobe's plugin). Since I was waiting long time for flash OS alternative, well, what a heck, I'll wait a bit more until Lightspark polishes out.
I use webm in opera/chrome. I just noticed the webm filter on youtube. Honestly, I could care less about gnash/lightspark. webm works fantastically.
I used to use it, too, but still, for some videos you have to have flash enabled browser. Plus, webm technology isn't yet mature enough for everyday use, for I had some problems and glitches, minor, but big enough to fall back to flash, after all.