It's an interesting question how an upgrade would have worked for me. Certainly Mac OS X has improved since 10.2 -- I've used it a bit on the computers of friends and I've heard that some of my frustrations have gone away.
I don't know how the hardware support would work though. I am fortunate that there is good Linux support for my model of PowerBook. Later PowerBooks seem less so, just by browsing Linux hardware support forums.
I expect to know better how the MacBooks work out with Linux soon. It seems to take six months to get new hardware to the point of usable support, at least for what I need to do.