How stable is C#?
C# is very stable. Even between major releases 1->2->3 there is very little chance of breaking source level compatibility. There is even less chance at the bytecode level (aka MSIL or CIL, not C#, but important to know). Microsoft has a very open development approach to C# including language meetings with various groups, including the Mono development teams. Microsoft is very open to feedback from the community. Open beta and CTP of Windows and .NET SDK make it easy to test upcoming versions and report compatibility problems. The result is a VERY stable language.