I will defer to the moderators, obviously, but I thought the answer was that once it is out there publicly, by CBS, then it is not considered a spoiler. I know the previews are allowed to be talked about in the show threads. I would think commercials are as well - since they should also be on the CBS site, correct?
Still, probably easier to keep the discussion in here until the show airs - at least as to commercials. I know Survivor is the only thing I watch on CBS, so I wouldn't see any commercials through the week. If I didn't want to be spoiled, I might be irritated in a show thread to see discussion of next week's show, even if the information is publicly out there, if I decided to go searching for it.