I'd say go for it!
I signed with my DD. At 7 months, she learnt the sign for water, but that was it, her only sign until she got to 12 months and then it ballooned. By 14 months, she had over 40 signs, but 16 months, it was over 80. At one point, she was learning a new sign at least every day.
Then she learnt to speak. And she lost all interest in signing. She will sign words if she already knows the sign, but is not interested in learning new signs. She is now 19 months and has over 100 spoken words (and even more signs!) which is over double the average for her age. She is already putting together two word sentences and beginning to put together three word sentences.
She was recently assessed for her language and I was told that she is "advanced" in her comprehension of language and her ability to communicate. We virtually never have tantrums from lack of communication either - she can say (or sign) practically everything she wants to. I believe that the signing has really aided her communication, as I found that when you sign, you slow down what you are saying, and you really make sure they understand, as you get them to sign back etc.
The research backs this up too - it says that signing can encourage language development, and further, some research says that babies who sign show greater intelligence at aged 8!
However, for me, that's not the real benefit from signing, I'd say the real benefit is that you get to know your child that much better. At 15 months, my child was able to communicate that she didn't like the dark, when she was feeling sad, when she had a pain etc etc. Things there's no way I would have known without, as she still can't say 'sad', 'pain', 'light' etc and her language skills are, apparently, advanced!
So I'd really encourage it. Have a look at a few other websites where signing mums talk, and you'll see that my child is nothing special - many parents who sign can tell similar stories!!