Hybrids like the Prius and Insight are image cars. You will never see you fuel savings surpass or even match your cost of entry (higher MSRP and 'market adjustments') unless fuel prices utterly skyrocket or you keep the car well beyond the normal 4-8 years.
Virtually all hybrids for sale in America today get well below their advertised MPG ratings. You can blame Honda, Toyota, the EPA, Hirohito, whoever, this is still a fact. I'm making an educated assumption that this is due to their country of origin; Japanese sit in gridlocks and stop-n'-gos while Americans highway cruise. We also use a/c and accessories more frequently and we treat the throttle like its going out of style.
Note one thing about the latest hybrids from Honda and Toyota - they focus on performance benefits and cutting-edge powertrain technology over raw fuel savings. They treat hybrids like Buick and Mercedes treated superchargers and Subaru, SAAB, and Audi treat turbos. They offer the performance of an 8/6 with the economy of a 6/4. People have stopped making pie-in-the-sky economy claims because they know they won't materialize. You don't see a commercial with the RX hybrid in a lush green meadow with fieldmice and Bambi; you see it colliding with an electric car and mixing technology.
The best way to save gas is still to drive less, share rides, combine trips, cut down on a/c use, don't cruise on friday nights or at the very worst, buy a new/used economy car to complement your nearly-paid-off vehicle, which probably isn't that much of a guzzler in the first place.