I think some people have a mis-conception about "commercial use". Commercial use is production for profit. You don't have to be a corporation. If you publish it, for monies, it is commercial use.
In the Adobe comparison someone brought up; I could buy a copy of student edition Premiere, I could use it in a class learning it, or make my own home videos that I wouldn't be selling or anything like that. I could use it to edit my wedding video or a friend's wedding video. As soon as I have used it to edit someone's wedding video, and they pay me to do it, it has become commercial use and I have broken the ToS/EULA/Faustian Deal.
Will anyone catch you for it? I doubt it since it doesn't watermark documents like that... as far as I know. Also, any profit you'd make on a novel is beans to Microsoft and not worth the cost of lawyers. However, you are still technically using it for commerce.
EDIT: What Microsoft has to say (Googled: non-commercial use office)
http://support.microsoft.com/kb/937676