CAMBRIDGE, MASS. — "That is not my presentation, although it would be very sexy if it were," said Ning CEO Gina Bianchini, as she took the stage at MIT's EmTech conference here, with someone else's Windows desktop blown up on a screen behind her. Alas, her presentation, a canned version of Ning's stump speech, was not sexy. Bianchini routinely talks up Ning, a set of tools for developing customized social networks, as if it were a platform, and takes audiences through a tiresome parade of the free websites created by her customers. MySpace, Facebook and LinkedIn are "walled gardens," she says — techspeak for an online service whose contents are tightly controlled by its owner. But listening to Bianchini, I couldn't help thinking that "walled garden" is code for "an idea I wished I'd come up with."