I'm about to finish my 2nd tank of gas - and the 1st honest one for moderate temperatures - since installing the Magnaflow. Not sounding the drums for their virtues but the combination of CAI and larger exhaust does look like it is gaining me somewhere between 25 - 30 miles in overall tank range. In the high teens that I was getting any gain is appreciated. It does require a small but noticeably less amount of go pedal to achieve a given acceleration, it is less prone to downshift on upslopes in cruise control, and it upshifts sooner when topping them out. I really wasn't after more power as much as better mpg.
On another note, I have received permission to spend some of the tax return on a rear bumper so I have begun research. With that add on, and my reduced income, my build should be pretty much completed.