I don't know about WDW, but a friend who used to work at Disneyland told me once that they collect all of the coins thrown into Snow White's wishing well & other fountains in the park and give it all to charity. I have no idea how much they generally collect, though - but I know I wouldn't want to have the job of counting it all!
I've seen kids at WDW fishing money out of fountains. Not on IASW of course, but out of smaller fountains that kids could more easily reach into. Parents never stopped them. For some reason that just bothered me.
Casst member told me on a recent tour that the 4 parks combined donate upwards of half a million dollars in collect coin a year. Listed off the charities as well, but I didn't write em down.