The Mac version of MS Office is reportedly better than the PC version. I can't verify this as I have never used it.
Macs come with most of the software the average user would want, but there are limitations in the area of games and specialized apps. There are workarounds, like Virtual PC, a program now owned by Microsoft.
It has a few slight advantages, the reviewing tools are a bit nicer, but overall there aren't any major differences except that the Entourage mail client is lousy for working with an MS Exchange-based mail system when compared with Outlook.