allnames,
performance wise I'm not so sure, on the 1.6ghz processor I've got (thinkpad x41 tablet) running fullscreen and throwing things around seems to be sluggish, but as I said thats likely my ubuntu drivers coupled with the higher resolution.
At lower res (800*480 especially) I am pleased with what I'm seeing so far, but obviously more will come.

Compatability wise (correct me if I'm wrong) clutter integrates with standard widget sets by becoming a widget itself, ie there is a way to create a GTK+ widget which is a view onto a clutter stage. There are bindings for multiple widgetsets but I haven't looked into this area yet.

I believe you can tell it to render pango code direclty onto a clutter surface but again its too early for me to get into specifics.

I'm extremely interested in checking out the custom actor classes themselves and seeing how subclassing and other interactions work, but so far I know I'm just skimming the surface

I can't wait to see it on an omap3 device itself and if required am more than willing to do what I can to get decent performance.

I'm even actively thinking about how best to get all this on the 810, and have even pondered about trying greyscale software GL

Clutter caught my interest, too.
For maemo 5 I'm considering changing the MediaBox rendering backend to clutter. Currently it's low-level GDK with most compositing done on the X server-side, but clutter on top of OpenGL might be great too.

mmmmm, liqbase natively runs too quickly on the laptop.
i need to find out whats happening with opengl.