One of the most publicized advantages of contributing to open-source projects are the (supposed) better odds at landing jobs. I think that people shouldn't be contributing to open-source just to land better jobs and then forget it, but I ask myself if that premise is true in the first place.
Have you ever been hired because of some open-source contribution? Or do you know someone who was?
IMHO - if you need to justify your skills, as in you are new, or have been out of work, then contributing to an open source would increase your credibility.