I've just finished tabulating my consumption for my 2000 Xterra from the past two years. I've got an excel sheet with all the data. I was interested in seeing if the 32" tires I got made much difference. Unfortunately, my two years of data didn't pan out to be enough since I was missing key months through the winter. This past winter was the only full winter of recording mileage in the two years.

As for the data, here are some figures:

Mar-04 - 14 mpg
Apr-04 - 16 mpg
May-04 - 16 mpg
Jun-04 - 19 mpg
Jul-04 - 18 mpg
Aug-04 - 19 mpg
Sep-04 - 19 mpg
Oct-04 - 19 mpg
Nov-04 - 17 mpg
Dec-04 - 18 mpg
Totals - 18 mpg (average for 2004)
Note: 2004 was all stock, stock tires.

May-05 - 17 mpg
Jun-05 - 18 mpg
Jul-05 - 20 mpg
Aug-05 - 20 mpg
Sep-05 - 19 mpg
Oct-05 - 17 mpg
Nov-05 - 18 mpg
Dec-05 - 15 mpg
Totals - 18 mpg (average for 2005)
Note: 2005 was stock up til November, Installed 32" (235/85R16) Tires (41lbs ea)

Jan-06 - 16 mpg
Feb-06 - 14 mpg
Mar-06 - 14 mpg
Apr-06 - 17 mpg
Note: All with 32" tires. This is the first winter recording milage. Once I rack up some summer driving, I will be able to tell how the tires compare.

All consumption listed in mpg.
Maximum seen so far = 21.9 mpg.

Distances adjusted for larger tire size using factor of 1.06, calculated according to rev/mile specs for tires.