Install 10.5.1 via software update > Something Doesn't Work > Argh > Combo Update >
Install 10.5.2 via software update > Something Doesn't Work > Argh > Combo Update >
Install 10.5.3 via software update > Something Doesn't Work > Argh > Combo Update >
Install 10.5.4 via software update > Something Doesn't Work > Argh > Combo Update >
That's when I stopped trusting Apple's ability to make delta updates that, you know, actually work!
They did apparently fix something to do with Software Update in 10.5.6 so perhaps i'm now just being overly paranoid
Saying all that every delta upgrade in Tiger worked purrrrfectly!