Furby,
This subject came up on the Yahoo milling group a few days ago. Here is what Dennis had to say:
A common misconception & maybe a bad choice of terms by the insurance industry.
An umbrella does NOT add ANY additional COVERAGES!
It DOES add additional LIMITS for the underlying policies, typically for the homeowner, the home and auto policies. In other words, if you have the coverage in your home or auto policy for say, $300,000 and you also have a $1 mil umbrella, you now can have a $1.3 mil problem and have your insurance take care of it without digging in to your pocket, provided it is a coverage already in your homeowners or auto policy.
So, NO ADDITIONAL coverages, just higher limits.
I have one and recommend it to all because I think it's a great buy and for most folks it's the only way to get over $1 mil liability (most homeowners and personal auto policies won't offer $1 mil or over).
-Doug