Ok, by now my first upgrade experience with Katmai is well-documented. So I thought I'd pass along some of my other experiences and some of the things I've learned.
My Vista upgrade:
I have a copy of Katmai Dev RC0 on my Vista box that I tried to upgrade last week. That didn't go so well. The only problem I had a chance to run into was with Visual Studio 2008 SP1. Katmai setup requires you to be on VS08 SP1 to install. And that's fine except that VS08 SP1 is in beta right now and I find it not only weird, but a little irresponsible for MS to require you to put beta software on your box. More on that in a minute, it's not as bad as it seems.
So my Vista upgrade was halted and I haven't gotten back to it yet.
My XP upgrade:
I have an XP box with Katmai Enterprise Eval RC0 on it. I tried upgrading this one knowing fully well that it's not supposed to be a supported upgrade path. I mainly wanted the upgraded tools and I would deal with the engine later. But I went ahead and tried the upgrade expecting it to bomb on the features checker like it did for the other 2 installs. Oddly enough, it didn't fail the checker at all. I ran the setup anyway thinking I may be in the clear, but I wasn't. While everything else installed just fine, the engine and SSRS failed. I'm not surprised at all, but like I said, I was a little when the checker didn't catch the SKU difference. OK, so now I have updated tools on my XP box. Or do I? Because the help section on SSMS still says 'SQL_PreRelease' so I don't know if they just didn't change that part or if it actually is a pre-release and nothing was upgraded. So I'm uninstalling the entire thing right now and I'll do a fresh install and see what happens.
As for my original 64-bit upgrade problem. I haven't nailed down anything yet, but a couple guys from MS have stepped up to help and it looks like it may be a SKU problem. Though we're trying to determine which direction the problem is in.
Now, for the good. I'm really loving the new command line setup in Katmai. And not only for installing, but it's also wicked for uninstalling. I really don't like having to go to control panel and clicking through all the screens to get rid of something. And I'll share one cool thing with you... Katmai setup gives you the command line syntax to uninstall when you have a problem. Here's what it gave me.