Many years ago, we saw Cal Ripken with his family in the parks. My wife is a Baltimorean, so she insisted on getting his autograph, much to my embarrassment. But, he was very gracious about it.
On the same trip, I stood in line behind Pierce Brosnan in Pieces of Eight; we were both buying swords for our children. Everyone behaved as if he was Just Another Guy, though the CMs working the register were quite twitterpated after he left.
Interestingly, Cal is a lot taller than you'd think. Pierce is a lot shorter! Neither had a Plaid escorting them.
I've also been to DLR during the long-lost ABC Preview Weekends, and WDW during ESPN The Weekend, but that's sort of cheating.