Parallels 4.0 for the Mac came out in January claiming lots of advantages over 3.0 some of which blog posts said didn't affect most people (I don't for instance have an eight-way machine with 8GB memory and aren't likely to have one any day soon).
So I didn't bother with an upgrade.
I was in any way getting used to the fact that I these days actually had a company-paid copy of VM Workstation on my PC (along with the copy I already owned on my home PC) and I had also added VM Fusion to my Mac and finally - after using VMs in Parallel when writing my book - had started using it in a small way.
(Somehow I always seem to use the Mac for forums and e-mail (and watching German TV shows from www.zdf.de) and use the Desktop with the still-going-strong 20inch Pro HP screen for real work involving the VMs - if that is I can shift my wife off it)
Anyway the fact that I was using VM Fusion most of the time, didn't push me in the direction of upgrading the Parallels.
However I was still curious about 4.0 so when I was offered the upgrade for EUR 31.89, it was time to get out the credit card.
The install is naturally over the existing 3.0 version but it still required the new code just as you were thinking it wouldn't.
Then the upgrade was going on it required you to change the state of your 3.0 VMs from suspended to shut down, which of course meant opening them all in 3.0 and then shutting them all down. Having done all that, the installation seemed to be needed to be started again (as one of them was still listed and thus Next wasn't available) and this time it required that all the VMs that had already been shut down (not the ones that had just been shut down but all the other ones that had been shut down rather than suspended). So those all needed to be started again and then shut down.
There followed yet another new installation run and this time it actually installed 4.0.
Then you have to upgrade your existing Parallel VMs to 4.0. Here you are offered Backup and Convert or just Convert.
Lazy as always (and I had two USB drives with copies on in any case) I just did Convert and this was OK for the first couple (it's a two stage process - the first stage is automatic but then you have to run setup for the virtual CD drive to get the Parallel Tools 4.0 installed) but then the next one stuck with the bar on step 4 of 4 showing completed (graphically) but the Next button still not available.
So I waited and waited and started a second conversion and that stuck at exactly the same place.
Nothing for it. A forced shutdown of the entire MacBook and re-start. Needless to say, perhaps, both those converted VMs worked fine. They had completed but just not informed their little installation routine mate that they had completed.
Anyway there you have it. I now have both Parallels 4.0 and VMFusion VMs on the MacBook. However since I replaced the hard drive with a 500GB one I can afford to have two different versions.
The only pity is that as this is a MacBook with a 2GB memory limitation, I can't have two many of the VMs open at any one time.
P.S. When doing the final conversion (a 15GB MOSS VM) I had a new variation on the theme. It stopped registering any change in ho far it had gone about half way through the blue bar showing progress in step 3 (of 4). This time when I restarted the MacBook after the forced close down, it first didn't boot but gave me the hard disk symbol only. Clicking that, though, booted the machine and clicking the MOSS image then took me right back to the same screen I'd had before (showing halfway through the third step) only this time it kept going and very very quickly jumped to step 4 and ready. Perhaps if I'd waited a bit longer before turning it off it would have completed by itself, but most probably it wouldn't have shown this and I would have still been forced to do a forced shutdown.
So the conversion works but the routine controlling it could be better. It could for instance let you close it down when it is stuck instead of forcing you to crash the entire system.