Like anyone else I'm happy when an application update goes smoothly. But in my case with WSS 3.0 SP1 this happiness is tempered *a bit* by the fact that because it went smoothly I am unable to give any assistance in the newsgroups to people whose upgrade to SP1 did not go smoothly.
(I think, though, on balance that I prefer it to work for me ....)
Anyway here is the sum total of what I did.
1. Took my slightly out-of-date (as far as the information in the Lists/Libs go) copy of a WSS 3.0 VM (running with 1GB of memory) and installed WSS 3.0 SP1.
It worked.
(At this point I checked the version number in Site Settings and updated my FAQ item with version numbers)
2. I turned that VM off and started the original WSS 3.0 VM (with up-to-date lists/libs = WSS 3.0 versions of the V3-related lists from the WSS FAQ site, which is still v2-based).
First I did the poor man's backup (but fast) by just Saving all four Lists as Template (with content) - so I could recover to my copied VM that I'd already updated.
Then I updated the original WSS 3.0 VM. That worked too.
(Note: I always do this kind of upgrade by accessing www.wssfaq.com to get at the download link. It saves time compared to going to the MS download site and searching)
So there you are. It IS possible to upgrade WSS 3.0 to WSS 3.0 SP1 with no grief.
P.S. A semi-related warning. If you are upgrading MOSS 2007 to SP1 level, you need to run both the WSS 3.0 SP1 and then the MOSS 2007 SP1. That's I suspect common knowledge and you probably don't need to be warned about it.
What however you may need warning about is that that installation means that you run the WSS 3.0 SP1 but then
uncheck the "run the configuration wizard" box. You then run the MOSS 2007 SP1 and only then (with both SP1s "installed" on your server) do you run the configuration wizard.
It says it somewhere in the documentation, but it's easy to miss so perhaps it's worth the warning here. Even if it only saves one person's grief it'll be worth my spending the extra time needed to mention it.