I actually had a center sneak play today. It was so weird an unexpected, that I had to talk it over before throwing the flag.
Center "snaps" the ball, it touches the QB's hands, then the center takes it back and runs it in for the TD. Since it never left the center's hands, it wasn't a legal snap.
When I explained the foul to the coach, he said, "Well, I didn't think it was legal, but I figured we'd try it anyway"
After the game, I spent about 10 minutes explaining illegal handing and the "fumblerooski" to a very interested and polite coach. I think it was a overall a good experience.