By the time we were at the end of the film, I was beginning to think that there weren't going to be any love letters to Apple in Up. The credits, featuring Russell's Wilderness Explorer merit badges floating by on a typed page, began to look somewhat promising. Sure enough, I spied a stylized and stationary "Spinning Pizza of Death," the dreaded Mac OS X wait cursor, on a merit badge just about at the end of the credits.
For those of you who are either Windows users or have been lucky enough to have never seen this infamous Mac icon (seen 3 times lifesize above), it's the Mac OS X equivalent of the hourglass in Windows. The SPOD (officially known as the Spinning Wait Cursor, A.K.A. the Beach Ball of Death or the Marble of Doom) appears when an application is not responding to events.
If you go to see the movie (which you should; it's funny, action-filled, and great for absolutely any audience) be patient and sit through the credits. You'll be rewarded by the sight of a SPOD on the big screen (it's after the two nuclear merit badges). If you're an Up-aholic, you can also check out the Mac game or the $4.99US iPhone game (link opens iTunes).
Update: Slashfilm has a photo of the SPOD (BBOD, MOD, take your pick...) merit badge in a detailed post about all of the Easter Eggs in Up.