1998 Honda Accord 2.3 4 cyl.: 23-26 mpg
It's actually kinda funny, because before the stereo I was getting about 21-23 mpg. So as the stereo's being done I also installed an intake and cat-back exhaust and when all is said and done I end up getting better mileage. I'm getting a header soon, and I'm interested to see if that'll help even more. I'm thinking it should since anything that helps the engine breath better increases its volumetric efficiency. I guess I'll find out soon enough though.
And that with a lead foot. I'm with phoneman on this one, my commute isn't as long, only 45 miles each way, and I take either the parkway or the turnpike and 70 is slow on those roads. 80+ is a normal speed, and there have been days where i've taken it well above that when I've been running late.