was curious what was more fuel efficient.. using a single or dual carb setup? (regardless of engine size)

any help, info, stories greatly appreciated.

I have had both a single (42dcn) and duals (36idf's) on my 1776cc with a mild cam and just the usual balancing of internals and getting compression ratios right.
The motor is in my Kombi, and on a long trip with the duals I got 28mpg. That was sitting on 95-100km/h.
Round town it does quite well also.
The single wasn't any better, and may have even been a bit thirstier. Powr comes on a lot more smoothly across the rev range with the duals so you don't have to work the motor as hard i found.
I think it's a matter of getting the jetting spot on.

Jetted correctly, a set of duals will give better economy. Doesnt sound logical until you realise with a single you have such long intake manifold runners that fuel can actually condense on the runners, thus requiring a richer ratio (more fuel) to make up for the amount that condenses.

At least I think thats what I read somewhere.

Doug is right.

Blue L is right about Doug ive heard

You should read this sermon by the excellent Bob Hoover:
http://osf02.ktu.edu.tr/~ulutas/hoover/dual.html 

often by increasing an engine's output you can reduce fuel consumption. sound whacky? sure, but when you realise you dont have to hammer a larger or tweaked engine as much as a small or stock one to get the same driveability, it obviously uses less fuel. (to a point of course :P)

I had a toyota crown once with a 2.8L six in it, which would get at best 350 to 400k's from 60L on the f3 freeway which I drive reguarly. it wighed 1550kg and had high gearing to suit.

I fitted a 3.0L Supra turbo motor into it and instantly could get 600k's from 60L of fuel onm the freeway!

of course if I gave it heaps it'd go through that 60L in 200k's :o