Fidicia
If you have, for example, $300k split evenly among three institutions, and in a form that's FDIC insured (investments typically are not), then you're covered for the full amount, $300k.
At the bank I used to work at they'd assist clients in selecting a way to distribute their money to ensure maximum coverage. If I recall correctly, my boss once told me that competing institutions would often exchange client info (with the latter's approval of course) to allow the creation of fully insured accounts at multiple banks.
Hey, who said banking's not all sweetness and light?