To me it seemed pretty apparent that they did the whole wedding dance thing just because it was such a YouTube hit that the characters who planned it thought they were being cool by emulating it, not realizing how played out it the whole thing was. It fits pretty well within the show's framework, IMO.
Creed was definitely great in the opening, but they did already sort of use this joke before. In the episode were Todd Packer took a dump in Michael's office (season 2?) and everyone walked into the office to smell and immediately ran out in disgust, Creed walks over and is like, "is someone making soup?" Still good gag, though.
Dwight burning Pam's friend was also great, but again not that original, since he burned that tall college bball chick when he and Michael went to NYC to hang out with Ryan. Dwight obviously has no respect for the party girls who don't have any inhibition, though he'll take them down when he feels the need to show off his prowess.
I really loved how Jim was the one who gave away Pam's pregnancy... it was a slam dunk that Michael was going to be the one to do it, and they at least did something different that made it pretty funny.