First, I installed Fink which brings dselect and friends to MacOS X. Fink let me install all the packages from Linux that I use. For giggles, I installed the Apple X server and ran KDE from Fink. It worked but felt sluggish. I also realized this was very pointless and stopped doing it after 5 minutes. Running X apps with the Apple Window Manager in rootless mode feels fast.
I have Virtual PC on my G4 Powerbook. It isn't fast but lets me test stuff in Windows when I have to. I used to work off a Macbook Pro in an old job and found VMWare Fusion and Parallels were fantastic when I needed to do work in another OS.
Overall I like it because its a UNIX I don't have to spend time administering.
I notice your usage patterns/programs are different than mine. Hopefully the perspective helps at least. Good luck!