If the left operand to the ?? operator is not null, does the right operand get evaluated?

As ever, the C# specification is the best place to go for this sort of thing.

From section 7.13 of the C# 5 specification (emphasis mine):

A null coalescing expression of the form a ?? b requires a to be of a nullable type or reference type. If a is non-null, the result of a ?? b is a; otherwise, the result is b. The operation evaluates b only if a is null.

There are more details around when any conversions are performed, and the exact behaviour, but that's the main point given your question. It's also worth noting that the null-coalescing operator is right-associative, so a ?? b ?? c is evaluated as a ?? (b ?? c)... which means it will only evaluate c if both a and b are null.