no, most guitars have the battery inside the guitar, the mono jack inserted into the stereo socket causes the 9v circuit to be grounded, thus allowing current to flow.
if you look at the diagram of the jack johnnyg drew, you will see that the 9v portion will touch the casing of the jack b4 it arrives at its own point of contact.
if you are holding the jack in your hand(and its metal ended jack)then you are touching ground. if you happen to make contact with the socket on the guitar while the 9v portion is touching it on the way in, well then you have just become a resistor joing 9v to ground.... hence the little shock(just a giggle ).
im pretty sure im right on this, either that or the last 4 years of electronic engineering in university have gone to waste
just trying to clarify the point i was making.
john.