Any guarantees about patents? Can using and extending .Net will cause in the future claims of software patents violations?
Microsoft Corporation and its affiliates (“Microsoft”) promise not to assert any .NET Patents against you for making, using, selling, offering for sale, importing, or distributing Covered Code, as part of either a .NET Runtime or as part of any application designed to run on a .NET Runtime. If you file, maintain, or voluntarily participate in any claim in a lawsuit alleging direct or contributory patent infringement…
MS still doesn't get free software, and probably never will.
Edit: My bad. "As part of a .NET runtime" means you can extend it. But I'd be no less nervous about using it because it is not a license, merely a 'promise' with questionable legal weight.