I have been signing to my boy Runako since he was 9 months old, and he is 14 months now.  Other than the rapidity in his language development - he has a signing vocab of more than 20 words, verbal vocab of the equivalent number (of course his phonics pronunciation is limited), and he is able to recognise many objects too, the more important thing is his emotional development.  I find that he truly enjoys himself when communicating a sign, and it does gives him a boost in his self-esteem, as can be obviously seen in his beaming face each time. 

Being an early childhood education academic myself, I have long read about the wonders of baby sign language, and now that I have experienced the benefits myself, I will definitely recommend all parents to take up this great signing course.  But of course, practise and patience plays a vital role in this aspect of teaching.