Apparently there's a bit of controversy over the McFlurry appearance in the last 30 Rock episode.
So far, I've read all of the product mentions on 30 Rock as jokes about product placement. Some of which were real product placement and some weren't, apparently.
I thought the episode where they were supposed to promote GE products like jet engines or whatever was pretty funny, and the joke isn't old to me yet. There's so much product placement going on now that there's room to mock it on an ongoing basis. There was an episode of Heroes where the teen character was tremendously excited to get a (particular model of) new car. Then it got stolen the same day and was never mentioned again, which I think is hilarious.
With the McFlurry stuff, it was so effusive that it was clearly a joke. It wasn't the funniest thing ever but I didn't groan either.