I have been teaching Matthew to sign for about a year now. I remember the early days of signing. He would just sit there and look back at me and kept thinking that he was never going to be interested in signing back at me. Then, around 9 or 10 months, he started signing 'baby' so that he could watch "Baby Einstein". I was so excited when he started to sign back!
Now he uses somewhere between 15-25 signs to communicate his needs. He has enough signing vocabulary to get most of what he wants or needs. He also can label animals (a lot of them) by signing.
I learned everything (well just about) that I did about teaching sign to my son from Laura Berg. She started Mysmarthands.com after teaching her daughter to sign at a very young age. I would have liked to take one of Laura's classes, but there are none around here. Luckily, Laura has been super kind in offering a lot of information on youtube, so that's where I went to look for ideas and to help me learn American Sign Language for babies.
The upside of my son learning sign language is that he has been able to "talk" to me since he was 9 months old. Usually he is just trying to tell me that he is hungry or wants his cup, but it neat to take my son to see my son sign "dog" when there is not even a dog nearby, simply because he heard a bark from somewhere in the neighborhood. I think that is awesome. Also, as I a former classroom teacher, I know that there are many different ways that people learn (http://www.ldpride.net/learningstyles.MI.htm Try out that site to find out how you learn). Many of the boys that I have worked with over the years are much more hands on. How can language be more hands on then learning language WITH YOUR HANDS! ***SIGH*** Why didn't I think of that while I was teaching all those crazy little first graders????
The downside....trying to explain to friends and family that the reason that my son only says "Dadahhh" and "dog" has very little to do with his learning sign language...and that it is not going to stunt his verbal language skills for life! My background in ESL taught me that learning a second language can be really tough! It is very easy to rely on what you already know to learn new words, but that is okay! As long as you continue to work on that second language growth. It is even okay to just listen for a while and get used to a new language. In this article by Judy Haynes, you can read about how a second language is usually acquired. http://www.everythingesl.net/inservices/language_stages.php
I highly recommend that you give sign language a try. No matter if your child speaks or doesn't speak....try it out!!!