I'm having problems with screen redrawing after I've applied a filter or used, for example, the shadow / highlights option. I have to zoom in (or out) of the image to make it apply (or probably just display) the changes to the image. This is obviously quite a drawback!
I have the GPU activated and turned that off but it didn't make any difference.
Apart from that I haven't played with it (demo version) much - yet. Looks similar enough to CS3 to be instantly comfortable but at the same time a few nice tweaks. Displaying the image without jagglies at all magnifications is great as is the zoom in and out function. Like the tabbed images too. May have difficulty in talking work into buying it for me in the current climate though...."off course I need the upgrade! how else am I going to re-size images for our intranet...?". Bit tenuous
Bridge also seems to have go-faster stripes now, which is nice.