So...unless new injectors and such would really improve MPG's...I don't see how people get anything significant over 20 MPG Avg. My friends claim to...but they have zero data to support the claims.
It can be done, but not without really working at it.

I've got data over 15k miles with quite a few numbers over 20 (details below). The biggest difference is:
1) the manual tranny gets great efficiency to start with, and enables lots of special techniques to save fuel (like engine braking or the ability to coast in gear for zero fuel use or with the clutch in for minimal driveline drag).
2) I've been paying particular attention to driving for best fuel economy. It takes me longer to get where I'm going, but I burn less fuel on the way. If you saw me drive, you'd probably find the numbers below more believable.

15,697 miles (adding 3% to odo for 265 tires)
699.5 gal (from the pump)
22.4 mpg average
26.2 mpg = best tank
18.5 mpg = worst tank (never got above freezing, some cold starts ~ 0F)
12 months

I got just over 20mpg when I bought the truck in july 2008 (previous owner did too). I probably got 1-2 mpg more from using all synthetic fluids, and the rest is driving techniques.