pharden- Can you give more info? Like a description of the spots.
We have a bunch of wild cherry trees (some of which are over the driveway) and some of the maroon-colored stains from their berries can be a REAL chore to get out. Literally have to abrade them away, polishing off paint until you get to a level that isn't stained.
Big trick here is to wash/clay BEFORE the stains really "take a set". And protect the paint with a sealant that keeps such things from "soaking into" the paint. The longer ANY contaminants sit on the paint the more trouble you're gonna have.