Delorme makes this mapping software that I used to use with my GPS receiver, but between Google earth and the fact that my GPS is equipped with maps kind of makes it moot. My Macbook doesn't have a serial port anyway, so it wouldn't work no matter what, and it's not like I really used the GPS/notebook combo when I had the capability. Google Earth is better anyway, in that it gives me a more realistic view of where I might be trying to go. That works great on my Macbook.
There were a few hiccups getting my Palm to sync correctly, but I've pretty much worked that out, and my iCal and Address book are populated sufficiently enough. The portability of my notebook negates some of the PDA's usefulness somewhat.
It doesn't talk to my iPaq at all, but that's a function of Microsoft locking Pocket PCs to Windows only, it was free, and it's a crappy PDA anyway. Heck, Outlook 2007 broke communication between my iPaq and my windows PC as well, so I can't fault Apple.
Other than that, I can't think of anything I can't do with my Mac that I can do on a PC. Oh, there's some corporate apps that only run on Windows/supported by my IT crew, but they have provided a Dell for that stuff, and I've pretty much made it all work on my Parallels VM for when I don't want to lug two laptops around. That's mostly an 'in a pinch' kind of thing.