The "is not" operator ("!is")This fixes a long-standing wart. Up until 1.5, the only way to check if an object is "not identical" to another object was to negate the result of "is". Since this is a very common thing to do when verifying that an object is not null, the codebase was scattered with code like "if (!(x is null))" which is as painful to read as it is to type.
1.6 adds the "!is" operator (which is simply syntactic sugar for "!(a is b)").