To poke or not to poke, that is the question

I don’t understand the semantics of poking on Facebook.  There’s a netiquette here that I just don’t get.  If someone you don’t know very well pokes you, what is the correct response?  Is it acceptable to poke several times back and forth?  I presume the answer are yes and yes but my inherent shyness makes me worried about doing the wrong thing.  Help, I’m confused…