It says a little bit about how fruit-centric my mindset is that I think of Richard Uva as "The Beach Plum Guy", rather as "Weeds of the Northeast Guy", considering that that book, which from what I've heard was a M.S. thesis project, is one of the very best weed guides for the region, a major scientific accomplishment, and, realistically, probably a much larger contribution to horticulture than anything involving beach plums will ever be.
I had a poster near Mr. Uva at an ASHS meeting once long ago--in fact that's how I learned there was such a thing as a beach plum, having managed to miss it entirely in several trips to Cape Cod.
Anyway, here's a link to a fairly good size overview on beach plums from Mr. Beach Plum himself:
Taming the Wild Beach Plum (Arnoldia reprint, via Cornell) PDF
Update: Oops...I mean Dr. Beach Plum. Looks like he acquired a Ph.D. since I met him. (Congratulations, Richard!)