By the way, I do use a "changing graphic" in one of my islands -- "Wha Sup?" It changes every day to a new graphic and text. I have set it up with 365 days. (although I only have about 100 graphics so far)... but it's cool and it keeps the site "fresh".
I'd totally add all graphics to an array, randomize it, and set its cache for 1 day; you'd never have to update a thing, lol