I googled around for this, and uncovered a rich seam of thought gone mad, including one complete lunatic insisting (in an academic journal, too) that nothing exists but quantum points, which have no relationship whatever to each other (and has also written about the secret rulers of the world in a book that an enthusiastic reviewer describes as more plausible than David Icke). Schaffer doesn't seem to actually take a position on atomism or monism -- here's another paper by him.
None of the material I looked at contained the argument (which convinces me) that the simplest descriptions of reality use complex entities (rocks, people, uranium, etc.), and that all the soul-searching over what really exists is just thought gone wrong.
Richard, a few thoughts and questions: what other people and papers did you look at?
IMO, Schaffer is the most interesting philosopher working in metaphysics today. He has a lot of interesting papers on questions of ontological priority and fundamentality. Well worth exploring, and too complicated to discuss in detail here (here's a link to all of his papers:)
In the end, he says, these are largely empirical questions, and that seems just about right. Many of his own argumets are of this sort (i.e., scientists finding ever deeper levels on the one hand, and...
(Last month's started a little late, I thought I'd bring it back to its original schedule.)
A monthly thread for posting any interesting rationality-related quotes you've seen recently on the Internet, or had stored in your quotesfile for ages.