From
the FDIC:
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">A co-owner’s funds in joint ownership accounts are insured up to $100,000, separately from any single ownership or other types of accounts of the owners if each co-owner:
• has equal withdrawal rights to the account, and
•personally signs an account signature card.
Exception:
Personal signatures are not required if the account is a certificate of deposit, a negotiable instrument, or is set up by an agent.
If these requirements are not met, the account will fail to qualify for coverage under the joint ownership category, and will be insured as the single ownership funds of the account holders.</font>
So opening an additional joint ownership account (a real one) is a way to go above the $100,000 limit at one institution.
But you are correct that all funds owned by one person and deposited in single ownership accounts in an insured institution are added together and insured up to $100,000.