Doug (and Jim), since CSS3 includes rgba (and hsla), I think opaque gradients would be a no-brainer (ok, maybe not – I came up with it last night when I was trying to go to sleep after two days thinking about it off and on). You could specify rgba(33,33,33,.8) for the top and rgba(33,33,33,1) for the bottom to get a dark grey gradient with slightly less opacity on the top than on the bottom.
I can’t promise anything since I’m just one member of the group, but it makes sense to me. And Doug, thanks for the suggested properties!! If everyone else could try to express how you’d like to define these things we want, that makes it a little easier to make concrete (because the concept’s not always difficult – defining it is).
As for “usable”? Some of it is now if you use Firefox or Safari. For example, I can use CSS3 selectors now if I don’t care about IE. I don’t think IE supports any CSS3 properties except the ones they invented and the group adopted (the only I can think of is text-overflow, but I may be wrong about that – it’s early).