The only thing I've ever hit was a raccoon. Was driving a Honda Accord and he was a big one. He jumped right from the trees into my bumper... was doing about 50 on a dark backcountry road. Scared the crap out of me. Poor little critter never felt a thing, I'm pretty sure..
I hit a squirrel when I was coming back from one of the recent really-bad interviews. (There have been two really bad ones...) I think he died instantly. Kinda hope so, even for a squirrel.