I guess while we're on the subject, I should mention that the "Jarrett's Room" sketches, the sketches which are supposed to webcasts of two college stoners, are done on Macs. Yep. They always used to do it on OS 9 (or at least one of the earlier OSs), but in the most recent one we can see they've switched to OS X. In Internet Explorer, if I recall correctly.
But, we'll never see those sketches again or Jimmy Fallon in the opening credits, as he's gone from the show. Ah, it doesn't matter too much, he wasn't that funny anyway. The Jarrett's Room sketches were terrible, but I think it was mainly Horatio Sanz's fault, as HE's a terrible cast member and should REALLY leave the show. Well, it's not a great show to begin with.
Oh, and in the Andy Roddick episode's "Mrs. Dalrymple" sketch (God, what an awful sketch), you can see a blue G3 iMac in the guy's room. You can probably find other Macs being used on the show as well, if you look hard enough.