We were discussing this before, and some of you were saying that with the newer Corollas, the MPG hit with the A/C on is negligible, someone said like
6 miles per tankful.
That may be in the very new models, though I'm skeptical, but since discussing it, I started paying close attention to it in these two cars and it's been pretty consistent. They both take about a 2 MPG hit on gas mileage with the A/C compressor running all the time.