I don't know about the the 1.25GHz models, but I've got a 1GHz 17" iMac G4 and while its capable of doing youtube videos, its not as comfortable as I'd like for daily use. On the flipside, I find my 1.5GHz PowerBook handles flash and YouTube just fine, so thats why I'm not sure about the 1.25GHz models, but it can only be better. My advice is this: Don't buy anything slower than a 1.25GHz model if you are going for a lot of flashed based internet. They are beautiful machines, and I know why you like them, but don't try and save a few bucks by going with an older one.