Having established that Microsoft's "it's not about Linux" schtick is transparently wrong - the area covered by the FAT patents is pure Linux, unchanged by TomTom, so any Linux distro with FAT compatibility would qualify - we then get a post from Jeremy Allison, who's well versed in Microsoft's approach to open source.
You must read the whole thing yourself - but in brief, he says that Microsoft has been putting all its IP deals under NDA because the cross-licensing of patents is disallowed under Section 7 of GPL 2. Thus, anyone who signs is disallowed from distributing any of the Linux kernel - so Microsoft has them over a barrel.
This explains the secrecy behind all the deals - which, lest we forget, Microsoft is promoting as examples of open sharing - and is building up to a situation where Microsoft can detonate a huge improvised explosive device under Linux.
What might save things is if TomTom prevails, negating the relevant patents - and there are good reasons to think it would, if it can afford to fight. If it can't afford to fight, then things get just that little nastier. As Allison says:
"Tom Tom are the first company to publicly refuse to engage in this ugly little protection racket, and so they got sued. Had Tom Tom silently agreed to violate the GPL, as so many others have, then we'd only hear about a vague "patent cross licensing deal" just like the ones Microsoft announces with other companies.
Make no mistake, this is intended to force Tom Tom to violate the GPL, or change to Microsoft embedded software."
Rupert Goodwins' blog was originally posted on ZDNet.co.uk.