Useful idea, although the implementation makes Safari stutter on a CoreDuo MacBook. I didn't check the internals, but I have a feeling that some value checks would benefit from caching.<p>Either way, I wouldn't deploy this just yet. But I also wouldn't deploy a PNG background that's position: fixed, because I remember it crippling old versions of Firefox on Windows..<p>I guess it depends, but us users with slow computers avoid websites that point out the fact that we haven't upgraded for 4 years.. I think the web is most definitely the one place where you can't presume everyone is on par with Moore's law. You just can't increase performance requirements according to your workstation (at least not on the client-side).<p>Remember any leet Flash websites from 2001 (besides 2advanced, err) where the stop-motion effect would reveal your CPU's inferiority to the developers machine? Exactly, me neither (there were a lot of them though).<p>I hope the plugin takes off, but it won't happen until it performs. Making websites slow on old computers is much like making type too small for the visually impaired.