My MB C230 is rated 23/30. I generally see 23-25 in mixed driving, 70% city/30% highway, so if I did nothing but city stop-and-go, I guess I'd be coming in at 22-23.
Highway, though -- While on walkabout from Hurricane Katrina, I ran between College Station and New Orleans several times. Open highway, 60-70 mph most of the way, premium fuel, with one passenger and with the A/C going. I saw between 30 and 32 then. Doing the same run in cooler weather and driving by myself, I'd guess I might get 32-33.