I think what ncaditya was referring to was the fact that when on gmail, the toolbar shows a page rank. Mine says it is about a 2.
However looking at the source code of the page, the email is all pulled in through external functions. So I doubt highly that PR would pass through. Plus even if it did, I would imagine they would use the No follow tag to prevent any PR leakage.
It's just the toolbar guessing. You see it happen on forum search pages all the time. I've seen forum search pages that were just created have a PR of 9. Those pages have no PR so I wouldn't worry about trying to capitalize on it.