Make sure you have all software updates in place. You didn't mention what version of OS X or how much ram you have or how much HDD space you have available however I have never had an issue with choppy play of YouTube videos rather using Tiger or Leopard.
Also what you can do is reset PRAM to clear the overall memory. Although some may say that flash is not great on the Mac OS it's not true because I have never had issues with flash and I have had only Macs for the last 10 years.
Although some may say that flash is not great on the Mac OS it's not true because I have never had issues with flash and I have had only Macs for the last 10 years.
Well, I don't think there was anything in my post that said I didn't run Windows PC's although I have not seen any difference however the OP was concerned about choppy playback of YouTube videos, not CPU use that's why I asked about how much ram, OS version, updates and HDD space as that can affect playback.
I'm having this problem as well. It's a brand new iMac, fully updated with the 3.06GHz, 4GB RAM, 8800 512MB. The only thing running was the WoW updater...and all that was using was bandwidth, and the YouTube video buffered plenty fast, it had the whole thing loaded and was still stuttering.
Maybe flash on OSX isn't as good as on windows, but for your hardware, it should be absolutely fine on youtube. I suspect its something related to your OS or hardware. Did you see any other display problem outside youtube or browser?