The only time I have paid attention was on a road trip (all highway) from ATL to Pensacola Beach, FL I had 407 miles on the trip odometer when the light came on and the range calculator read 0 miles. As a side note, I had the AC on the entire way and set cruise control to 70mph. I have the V8 4WD Limited.
When I filled up I remeber the tank actually has about 2 gallons left when the light comes on, so I guess at 19MPG I could have driven another 38 miles before I was really out of gas.
I didn't want to find out that night anyway, I was ready to check into my hotel room and have a brew.