Microsoft is claiming that TomTom is violating its patents, and the specifics here seem to put other Linux-based devices like the OpenMoko FreeRunner at risk.
The suit alleges that several of TomTom's products, including some that are Linux-based, infringe on a handful of Microsoft's patents. Several of the patents in question relate to car computing systems and navigation, but there are also two that cover Microsoft's FAT32 filesystem. If Microsoft begins to systematically enforce its FAT32 patents, it could have broad ramifications for the Linux platform and for mobile device makers.
Help the End Software Patents campaign's efforts to disarm Microsoft's aggression by digging their story about it.
The article at Ars Technica has more details.