Unless things have changed in the last year, the fastest way to go out and grab a quick smoke (If flying UA...) is to use the security area between B and the E/F connector. It never took me longer than 15 minutes to get back in, and there is a covered smoking area just outside of the door.
As I no longer commute through ORD on a weekly basis, things certainly could have changed.
If you do a search, you'll find a thread from last year that lists all of the airports with known smoking areas.