Of course, Sally isn't just any ordinary single mother, she's one beloved by at least one Greek god. A forbidden love affair with Poseidon produced Percy, who just might be the boy to fulfill a prophecy. Sally tries to conceal Percy's identity from the gods and from himself, but of course that never works.
The Olympians cast so far include Uma Thurman as Medusa (I know, right?), Pierce Brosnan as Chiron, Melina Kanakeredes as Athena, Kevin McKidd as Poseidon, and Sean Bean as Zeus. They're still looking for a Hades and probably annoyed Clash of the Titans nabbed Ralph Fiennes as theirs.
I share Peter Martin's doubts that this will be the next Potter (I think that's a one time thing), and I'm so-so on the story because it flouts mythological convention and gives the man-disdaining Athena a daughter. But I am a sucker for a lot of the cast members (especially McKidd and Bean), and the idea of McKidd and Keener being so overcome with passion that they flouted the decrees of the gods? That is the stuff Greek myths are made of, so who knows? It might be pretty fun.