Definately go for it!

My parents are deaf so I am fluent in sign language. I taught my DS sign from around 4 months. It wasn't until 12 months that he finally 'got it' (he was premmie so he was 10mths corrected age). It was fantastic to have him tell you what he wanted. If he wanted more dinner, or if he was finished. He still uses some signs now, although he talks very well for his age. I did find that once he started saying words, he preferred to say rather than sign. My sisters DD however was very different. She was signing from around 7 months and continued to learn sign even after she was saying words. Although at this stage it wasn't necessary for her to sign, she sure was a great party trick!