I'm thinking that a bunch of the iphone mockups that I've seen end up with the same shared components - toolbars, tab bars, status bars, etc. Those standard components are really the same objects, just in a more hi fidelity fashion.
Also, AFAIK with those tools, once you export, there is no way to keep the wires and mocks in sync, right?
I've experienced times in a consulting shop where both the mocks + wires are being iterated on simultaenously (mostly because the product guy would use omnigraffle where the designer would use photoshop) - leading to mocks + wires that just didn't jive with each other. This created confusion among the dev, design, and product teams about what specifically we were building, leading to increased time to market.