Found out today I'm getting a set of the Gerbing pants for Christmas. Will be great with the jacket liner and gloves that have already kept me so warm and toasty sometimes.
Gerbing said the pants liner shouldn't be worn like a set of long underwear; that a set of long underwear should still be between the liner and your skin. They also said the outer pants were commonly still worn over blue jeans. All that being so it seemed that layering would be more effective with the outer pants rather than the liner. They're supposed to be ok in wet weather should you trouble in to some and if you start on a day that's cold and then warms up some it'll be a lot easier to lose a layer of gear and electrical harness if it's outer wear rather than underwear.