I see an ad for iListen on the side of this page, but my main reason for maintaining a Windows machine is Dragon Naturally Speaking, which I think is way ahead of any Mac speech recognition package at this time. The only other reason I can think of for keeping a Windows machine: frustrating incompatibilities that still crop up between MS Office on Windows and MS Office for Macs, especially in Japanese.
Parallels Desktop - A True Killer App for Mac With New Beta Features