Nvidia confirms the GTX 580

[Sam_oslo]

That would be quite unexpected and probably not a wise choice. Nvidia needs to tell their potential costumers that they have something better on the horizon because otherwise it's a big risk they'd be jumping ship.

Yeah, but those "potential costumers" doesn't believe it anyways, after those wood-screws in last round.
But seriously, keeping it secret to surprise the competitor is nothing new, and it has it's advantages that may be more than disadvantages you mentioned. In case, it will come right at time of the release of Cayman, to avoid those concerns you mentioned.