So:

Companies like Tomtom use FAT as a filesystem along with the Linux operating system.  Microsoft — silently most of the time, except for in this case — get these companies to sign cross-licensing contracts to use FAT.  But these deals violate the GPL, which the Linux kernel uses as a licence.  So when these deals eventually become public the GPL lawyers will do MS’s dirty work for them: sue these companies out of existence.  This then, through fear of litigation, effectively forces these companies, and others, to use MS embedded technology instead of GPL/Linux technology.

Getting the GPL’s lawyers to do MS’s dirty work is advantageous to MS because MS won’t have to suffer the costs of litigation themselves, and no-one will scrutinise their somewhat dodgy patents, especially the FAT patent. The GPL lawyer will only look at the cross-licensing contracts, not the actual patents these are based on. Also, if MS openly force companies to either us MS technology through their FAT patent, companies may shun FAT altogether, much to MS’s detriment.

So, MS’s forcing companies to sign cross-licensing contracts and pay MS money with dodgy patents. But, because of these cross-licensing contracts, this means these companies will violate the GPL, thereby ruining the company eventually when the GPL lawyer become aware of this, all because these companies chose not to use MS technology.

This is all pretty shrewd, and it’s based on their FAT patent — which is arguably valid, at the moment anyway — they can attack companies that choose to use non-MS technology.

Edit: http://blogs.zdnet.com/perlow/?p=9594 this is a much better article.  It claims MS are trying to enter into Tomtom’s market, and so forcing them to use MS technology would suit MS just fine.  The guy also used to work for Unisys, and asks why the whole embedded market doesn’t do what the desktop market did when Unisys tried to assert its patents on the GIF file format: shun the GIF format and agree on other file formats, i.e. JPEG and PNG in that case.