On my way to band practice last night I spend some time doing 60 about 3-4 car lengths behind a Scion xB. I was amazed to see my MPG went up about 10 MPG (showing 45-60 on the Scangauge compared to 35-50 before and after) while I was behind him. I have tried drafting in the past with inconsistent and generally disappointing results but this was amazing.
I think the trucks and stuff I had been drafting behind before probably had too much ground clearance and my car was just getting hit with all of the air from underneath. The xB however is a complete box and is low to the ground so there is very little "normal" air coming from under the car. I also don't feel like a jerk cruising along behind the xB like I do when I am behind a semi in their blind spot.
So now you know, if you have the chance to follow a toaster, do it!