I have some mpg numbers.
I only use premium fuel. 91 octane is the max here in Cali. I've tried different brands gas and they all seem to produce similar mpg for me.
This is on a SC, with Hondata, and 9 psi boost 3.15" pulley
24-25 mpg 50% highway, 50% City. Driving normal, 85 mph on the freeway
20-22 mpg 100% City Driving
17-20 mpg (maybe even worse) Driving hard all the time.
Since going to Hondata, my gas mileage has actually increased. I'd say it has went up about 1-2 mpg. If I'm driving on the freeway at like 70 mph the whole time, I bet I could easily get over 25 mpg. I have trouble doing that though
This is on an 04 TSX with 115K miles. Keep in mind that the SC has a bypass valve. So when you are not on the gas, it is not adding any extra air and you can drive normally.
__________________

K-E-N-N-Y
04 TSX CGP 5AT Auto - 265hp / 199tq
Hondata K-Pro / CT-E Supercharger 8 psi
Advan Kruezer Series X...a few more mods here and there