I recently bought a Mac Book Pro since I can now dual boot OS X and Windows XP. The only real issue that I've had is that OS X, like most Unices likes to set the hardware clock to UTC time. This causes the clock in Windows XP to be off by 5 hours (I'm in the central US timezone).
I recently discovered a registry tweak that will tell Windows to interpret the hardware clock as UTC time:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation]
"RealTimeIsUniversal"=dword:00000001
Just save the above reg script into a .reg file and import it to set your clock to UTC time. You can still set your timezone for the clock and have the correct time displayed. This can also be usefull if you are dual booting XP with any other Unix variations that like to set the harware clock to UTC. I usually run Linux and such in VirtualPC/VMWare so I havnt actually tried it with Linux.
Update:
It would seem that there are still some issues with this:
http://blogs.msdn.com/oldnewthing/archive/2004/09/02/224672.aspxIt seems to work most of the "time" for me but 1 or twice a day the clock changes to the timezone offset again. I just have to do a w32tm /resync /nowait to fix it. My suspicion is that the clock applet in the tray is monkeying it up.