Got 2 on mine, one under the seat and one on the infill for the fairing, left hand side (02 foxeye) that has a rubber waterproof cover, it might be worth adding in a relay too, so that there is only power to the sockets when the ignition is on, I did the same with a relay for the heated grips too so no one could switch them on while I was away from the bike and flatten the battery, same with the sockets, you don't want any little tyke shoving anything in the socket while it's live.
I've ordered a twin socket, one cig socket and one twin usb in one unit, perfect for sat nav and mobile phone charging etc on the go :-)