Getting an MS is a sign that the candidate wasn't particularly good before getting one, because of the various reasons people get an MS. And it's not like they became a better developer as a result of getting one.
The way to determine this is by measuring actual performance.
With more information, like why or how they got an MS, the probability distribution changes. My impression is, there's a set of dimwits from a dimwit part of the industry that decide they should get a Master's in order to better their career. As opposed to, say, getting one right after school because you didn't want to enter the real world, or because a 5-year MS seemed like a good idea, or being brainwashed in general about the value of formal schooling.
Don't ask me! I never got a Master's, and if I did get one, it wouldn't be in CS. In general I think work experience would inform your course selection or the decision to get an MS in the first place. That's pretty much the main way it would affect it.
