Yeah, I think three Spider-man movies should be more than enough. What with the last one kinda sucking (Oh no he didn't! Oh yes he did!), and Tobey Maguire getting super-fat.
I mean, he's already fatter than Shatner in The Final Frontier (that's the Star Trek movie no one liked, wait...), and it's only been one sequel so far. I don't think he'll make it past three, let alone six at this point.
Anyway, I suppose the only reason to make all those super-hero movies is to milk the fanboys' lust for nitpicking the costumes of each sequel's villain du jour, so it's okay with me.
SciFiWire has Sam Raimi's take on it:
Spider-Man director Sam Raimi told SCI FI Wire that Sony Pictures plans to make six of the comic-inspired films, and that he'd consider helming them if he feels as strongly about them as he does about the upcoming third installment.