We've successfully taught our DD the sign for sleep (hand on ear, head tilted as if you were asleep), for "more" (as in, more food please!), which is open hand up to mouth (although she actually says 'more' now too), and the sign for poo, which we hope will help out with TT (she squeezes her nose, in a stinky kind of way, when she's done one). She hasn't really got the hang of any other signs, we're certainly not forcing them on her though. The ones she knows, she uses ALL the time, and always appropriately... its brilliant, and I think she really enjoys it that we totally understand each other. I borrowed the book 'Baby Hands" from the LIbrary, and that was full of info. I'd go for it, for sure. We started just recently, when DD was probably about 14 months, but I think she would have been ready for it sooner.