Microsoft has very kindly posted the new royalty-free-but-with-conditions license and a FAQ on its website. They’ve also directly, sort of, dealt with the open source question in the FAQ:
Can the license be obtained for use in Open Source products?
The license doesn�t make a distinction between open source and commercial software products. However, some open source licenses have terms that are incompatible with certain provisions of the Office UI license which are necessitated by the type of rights Microsoft is granting. Each developer should examine the open source license he or she is using to determine whether the Microsoft Office UI license is appropriate for his or her desired use.
OK, I’ll bite. Which licenses are incompatible? Any license mavens out there want to comment on what this means with respect to the GPL, Apache, Eclipse, and Mozilla licenses?
If it were not compatible with the GPL or the others, then this might have some implications for the new, open Java and its various windowing libraries, should they ever wander too close to the Office 2007 look and feel.
Update: Pamela Jones over at Groklaw answers my question above in the negative, saying
Perhaps it would be more honest to say virtually *no one* in the FOSS community, your principal competition, can use this license, and for sure the GPL need not apply.