Basically, not all parts of Mono are covered by the ECMA standard - said standard is the only part covered by Microsoft's community promise. However, you'll often hear people say that that's okay because Mono programs included in some Linux distributions only use those parts of Mono that are covered by the ECMA standard, and therefore, are safe to use according to Microsoft's community promise.
Well, The-Source.com investigated this claim by analysing five popular Mono applications, and their findings paint a grim picture - all of them use namespaces not covered by the ECMA standard, meaning they can still be sued for patent infringement by Microsoft, and so can the distributors that include these programs.
- Banshee: 165 refs
- Tomboy: 36 refs
- F-Spot: 131 refs
- Do: 56 refs
- Gbrainy: 31 refs
This indeed sounds rather problematic. Up until not too long ago, Microsoft did not actively participate in any patent infringement lawsuits as the aggressor, and as such, you could argue that the threat was minimal. However, Microsoft maffia'd several companies into signing patents deals with them, while flat-out suing Motorola.