http://www.fifa.com/mm/document/affederation/administration/50/02/75/discoinhalte.pdf - The reference I quoted is on page 30.
Also of interest are the recommendations set down in rugby. To highlight how serious they view biting, the only offence with a more serious punishment is the physical...
I had a look at the FIFA recommendations, and they don't have anything listed for biting (probably because it happens so rarely). However for spitting (in my opinion, a similar but slightly less severe offence) the recommendation is at least six matches. I think ten for Suarez is pretty much...