My '99 LS with 167k (well maintained and no mods of any kind) gets 13mpg in the city (5-10 minute trips, stop and go, staying under 40mph etc. Light foot.), and 28.5mpg on the interstate with the cruise set near 80mph and the a/c full blast 9 or 10 months out of the year. I wish I could slow it down to 70mph to see if it would hit 29-30mpg on the interstate, or even higher if I would stay on back roads going 60mph--those speed trap infested back roads are like torture though.
As good as the mileage is, it kills me that 80mph = 2,600rpms. Imagine if 80mph was only 2,000-2,200 rpms like it is in most cars....