Just got the upgrade last night and played around. It did not overwrite PSP9 even though it was an "upgrade." But at the same time it loaded all of my "stuff" from PSP9 into the new folders for X, so I now have PSP9 and PSPX available on my computer for use. I like that for now, but I am sure I will probably quit using PSP9 altogether and get it off my computer.
A few quick comments:
I LOVE the high pass sharpen and the tooth whitener

Also the blemish fixer--much easier to use than the clone tool for that purpose (clone tool is still there though, as there are plenty of uses for it).
The setup is a bit different but didn't seem to be too different that I couldn't figure it out. Looks very "Corel-like." (I have Photohouse--old version).
The pictures on the layer palette are pretty neat but I am not sure that I feel they are great. I haven't figured out if I can make them bigger or zoom in, but that would be helpful, b/c sometimes if the content on the layer is small, I can't see what it is anyhow. Still better than scrolling over to see it.
On the downside, those were the only MAJOR things I noticed in the upgrade that were important to me (although I know from Tracy's post that there is now a contact sheet you can make easily, which could be a big benefit to some). I also only haven't played a ton so there may be more to find. But I didn't see much in the way of more tools (makeover and object remover were the only ones I noticed) and added shapes/brushes/etc. Personally I was REALLY hoping for more preset shapes and things like textures.
The color balance tool is different than in PSP 9 but I haven't played with it yet to see if I prefer it. It looks more in depth, I guess, but may just be different, rather than better. Don't know.
I hope this helps people. Those are my *subjective* opinions

I would love to hear what others think if they have the new program AND were using PSP9. Thanks!