First, my D2's fuel gauge is a bit strange, and the amber warning light comes on roughly after using up about 20 - 21 gallons, while I belive the gas tank capacity is 25 gal.
That said, with 80/20 hwy/city driving gently, I get 300 - 310 miles with mid-grade until the amber light comes on, and I fill till the pump automatically shuts off, which is roughly 20+ gallons. At $3.45/gal as of 11/6/07, things are beginning to add up.