From time to time, people write to licensing@gnu.org expressing concern that Mono and dotGNU -- both projects that the FSF publicly supports -- infringe on Microsoft patents.
At GNU, we want to have free implementations of every language or platform that users use, and that includes .NET.
Due to the menace of Microsoft patents, you should try to avoid writing software in .NET. But if you do, we want you to be able to run it on free software.