Last May, when I made a reservation for my Prius, gas was pushing $4 per gallon. The tipping point for me was filling the tank on my minivan, and the total was over $50 (as I recall). At the dealership, the salesman was predicting $6 per gallon wasn't far off.
Today, local stations are selling gas for $1.95 per gallon--less than half the price six months ago, less than it's been in the last 2-3 years. I filled my Prius tank for approximately $15.
I'm feeling inappropriately smug, right now, because while you alls' gas bills have fallen--they haven't fallen as much as mine has!
And when the inevitable happens, and gas prices bounce back up again, I'll still be saving money.