Great, the US Patent Office confirmed Microsoft's patent on the FAT file system:
As part of its review (Re-Examination), the Patent Office initially declared the patents provisionally invalid (Non-Final-Ruling) due to "Prior Art". The decision now made, however, is final and Microsoft receives a so-called "Patent Re-Examination Certificate" from the USPTO for both patents. The Patent Office finally determined that the FAT file system had been a new development and therefore patentable, Microsoft further announced.
We can therefore wait and see when Microsoft will use the patent to take action against open source software that uses or supports FAT file systems.