I've seen a study (sorry don't have a link now) where it was shown that MSM isn't being metabolized by the body and it's just being excreted in the same form as it was taken. So it's very questionable if it's true that MSM is a good source of sulfur. However I believe it has some other benefits (I love it for its nootropic effects and I keep it for those times when I need powerful mind-kick to complete some complex work - I'm programmer).