The Porsche Boxster will delight owners in lots of illicit ways, but the pleasures of visiting the gas station are totally legit.
The Boxster's one of the few sportscars we can think of with such a high fuel-economy rating. In either the base Boxster, or in the Boxster Spyder, the EPA rates the Porsche convertible at 20/29 mpg when it's fitted with the PDK dual-clutch transmission (which the EPA thinks is an automatic). With the manual gearbox, it's still scored at 19/27 mpg--close to the numbers you'd get in a full-size sedan like a Buick LaCrosse, and about double what you'd see in a Lamborghini Gallardo.
Stepping into the Boxster S doesn't sacrifice that much more fuel. The S gets 19/26 mpg from the EPA when it's equipped with the manual shifter, and 20/29 mpg with the PDK.