Well one issue with grid-tied systems is that when the grid is offline they provide no power (they explicitly don't want to back feed into the power lines and kill some lineman who things power is off). So one of the certification issues is to make sure that your inverters recognize that state and shut down.

But a side benefit of putting in the system was we did a lot of electrical panel work, and as as result put 8 circuits on to a transfer switch (the incremental cost was the transfer switch and the electrictian's time wasn't materially affected.) So when the power does go out we can fire up a generator and switch over to gen power easily.