On the other hand, "may be a patent problem" is an appropriate description of any recently written software.
I would expect Microsoft to fulfill its "Linux violates n Microsoft patents" threat before it does the same for Mono: Each programmer using Mono enhances the .NET ecosystem, while each Linux installation degrades Windows' market share.
http://en.wikipedia.org/wiki/Mono_(software)#Mono_and_Microsoft.E2.80.99s_patents
And it looks like the Windows Forms and such stuff may be a patent problem.