The NAVI is probably more mac compatible than other brands, due to the fact that you use a standard SD card to input data. I use a Powerbook G4, and have no problems.
I run a windows emulator to run RealSpeed, but you could use GPSActionReplay, or GPSResults instead. Both of these run natively on the mac, and have all the functions you need.
The only problem with using a mac is updating the firmware, but my emulator handles that fine. You might need to borrow a friend's PC if you don't have a windows emulator, but updating firmware is something you might do once every six months.
Modern (intel) macs can run boot camp, so can boot windows natively if you don't have an emulator as well - once again you only really need to do this every six months or so.
So the short answer: The NAVI is (mostly) Mac compatible.
Sflack, think you might get some people disagreeing with you there, check this thread,
www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=36085
i use my navi with my macbook...
v. easy 2 use.. three options
1) bootcamp
2) parrells emulator
3) a mac based gps program... such as 1 i got off the apple website 4 free =) legit.
its called trail runner. not as good tho.
btw mac is the best computer ever. PC r so **** and boring