I switched from Castrol GTX to Mobil 1 in my wife's car, and I also noticed an increase in fuel economy. The synthetic is, of course, more expensive but I recoup my cost by getting better fuel mileage, and I can now go 5000 miles between changes instead of 3000.

I won't use synthetic in my 4Runner because it's had the regular stuff for just under 250,000 miles, and I hesitate to make any waves. It also likes to burn a little oil, and it would burn much quicker with synthetic.

Keep that in mind, by the way - if your vehicle burns or leaks oil at all, it will go through synthetic a lot quicker than regular oil.