Good question Creaker. I think I got my figure from a Bloomberg talk right after the Aurora incident. Knowing how politicians play with numbers, I did a quick check. According to the CDC there were 11,400 homicides by firearms in the US in 2008. Not sure about drunk drivers, but would imagine they are more random, which would raise your odds of being affected by a drunk driver over a gun toter, unless your are maybe involved with shady characters with guns.
http://www.cdc.gov/nchs/fastats/homicide.htm