Within the US/Canada never had a problem, the only issue occasionally been the failure to post the 500 Platinum Amenity points, but the actual hotel stays/points no issue. Outside of the US/Canada though, almost the reverse! I would say that half the time they don't post and half of those that do, do so incorrectly. One thing that has happened a couple of times is that the currency conversion used to work out the points has been ridiculously low, to Marriott's credit, everything has always been resolved. But its a major flaw in their program and a major hassle.

I personally think that if you have made a reservation through Marriott.com, your SIL/GLD/PLT number is on that reservation then there should be some kind of guarantee that the points will post... if not, a 1000 point bonus or something. Starwood on the other hand never had points fail to post, anywhere in the world, longer than 48 hours after checking out... so is possible!