2000 Boxster base, 2.7L 76K miles
I'm checking my MPG just like you.. every time I fill up, I pull my phone to do the calculations
I was getting 16-18mpg, and I drive about 40/60 city/HWY.
For last 2 tanks I'm up to about 20mpg thanks to technotorque, but then again.. I cruise at over 3K rpms
Sasha