Microsoft is starting to rattle some sabres:

An excerpt from
http://money.cnn.com/magazines/fortune/fortune_archive/2007/05/28/100033867/
(Found at lwn.net).

But he does break down the total number allegedly violated - 235 -
into categories. He says that the Linux kernel - the deepest layer of
the free operating system, which interacts most directly with the
computer hardware - violates 42 Microsoft patents. The Linux graphical
user interfaces - essentially, the way design elements like menus and
toolbars are set up - run afoul of another 65, he claims. The Open
Office suite of programs, which is analogous to Microsoft Office,
infringes 45 more. E-mail programs infringe 15, while other assorted
FOSS programs allegedly transgress 68.