Dont do it unless you want to make inroads into academia or better your chances for working at Google/Microsoft/BigCorp. I have a BS with about 5-6 years of experience and I lead/manage a couple people with MS degrees. In other words Ive found that having an MS makes little difference as a signal to an employer in most cases if you already have a BS in CS. Your ability and connections seem to be the most important thing so if you think an MS will enhance either of those it might be worth it but it also could very well end up being money down the drain.