I live in Phoenix, so I can comment directly the the mileage in the summer months. My average was 45.67 MPG for my first six "Phoenix Summer" tanks, but I have since learned to drive for increased efficiency, so I'm betting I can keep it in the 48-50 MPG range this summer.

Using the A/C in a Civic Hybrid "does" bring the MPG down, but really no different than any other car. Your misinformed co-worker loses about 2 MPG in his Escalade when he uses the A/C too (don't tell him though!!)