Well, ok, the roar may be more of a meow ...
Fact is, I finally managed to get Tiger running satisfactorily - phew! Now I know how the Windows world dreads system upgrades. But before you start lambasting - the trouble wasn't Tiger's fault, mostly!
The first difficulties appeared yesterday evening when the installer resulted in irrecoverable errors - hard drive trouble which not even a Disk Repair with the Disk Utility would eliminate. But that's exactly what DiskWarrior did in two hours hard work! Believe me, I was getting rather nervous there and have rechecked my backup now!
The next problem arose with Virex 7.5, which is a hitherto entirely redundant virus protection software available as part of .Mac. Just so you know: I never ever had it report any infections whatsoever, and my Mac is online virtually 24/7. But what it did do is, it had a process running called VShieldCheck, which ate all available CPU resources! Very nasty! But nowhere on .Mac did I find any explicit info that this would happen, and that Virex 7.5 was not compatible with Tiger. Rather annoying, that.
The next big problem to solve was Mail: The mailbox import went rather smoothly, if importing more than 54'000 messages can go smoothly (years of usage, you see). However, when I tried to lock at any individual message, the app just crashed on me! After some lengthy debugging, it turns out that PGP 8.1 and Mail.Appetizer were the joint culprits!
But now, it's finally up & running, yay! Only, I miss another 3 Gigabytes from my HD - I guess Spotlight and other extended services do take their toll. Widgets for instance are just great! Here is the first specifically Swiss widget already (a rain radar map).