The speed difference alone (I have an Intel Mac) makes the CS3 upgrade worth it. And I like the new photomerge in CS3 although AutoPano Pro does a little better job.
Haven't tried Lightroom since the original beta came out. I'm "in love" with Aperture and now that I've figured out the RAW workflow with it all I need PS for is photomerge, layer work etc.
The Aperture luminanace 1/4 tone controls act the same as curves in PS and I understand how they affect the image way better then I ever did with curves. I think the highlite/shadow/saturation tools are just flat out better then PS as well. I hope that Apple will build plugin/camera profile support and better noise control into the next version.