I had been delaying the upgrade to the latest Mac OS, and — it turns out — for good reason. This was the most painful OS upgrade I can remember. Luckily, I had cloned my main drive before I started the operation. Unluckily, the cosmic forces of contingency hammered the interactions of my drive, the installation DVD, and the back-up drive, such that I ended up installing the OS about three times (I lost track after a while). Once it was all installed, the system wouldn’t boot; evidently, it needed its PRAM cleared. Then the usually-silky-smooth Migration Assistant pooped out partway into the transfer of files from my back-up to my main drive. I’ve been doing the rest by hand.
On the other hand, tomorrow probably won’t be worse than today.