Update 5:30p: VMware's Pat Lee has acknowledged the problems on the serial-number system and has posted a universal 30-day trial license code and download link to allow users to install the new version.
I never was able to upgrade to a paid version of Fusion 3.0, so I downloaded a demo version and 2.5 hours later received a 30-day serial number.
Installation was trivial, but now I can't find my old version 2.06. That would be bad for people who are trying 3.0 and decide to go back to an older version. I tried a Spotlight search, and my older version is nowhere to be found. That's not good. Has anyone else making the upgrade experienced this? Update: Commenters make it clear that 2.0 will automatically be removed when you move to 3.
I'd already upgraded to Windows 7 on version 2.06, so the same OS came up fine under version 3.0. One of the advantages of 3.0 is that you can assign multiple cores to the app, and since I'm running on a 2 x 2.66 Dual Core Xeon I assigned 2 cores.
Start-up was faster than the old version. About 45 seconds to the Windows 7 desktop, and a few more seconds to bring up a couple of gadgets and settle down. Launch times of apps seem pretty fast, but I don't find the difference dramatic.