It's up to you. With DS we told no one at all until 13 weeks but this time we had to tell people early as it was Christmas and everyone would've known when I wasn't drinking anyway! I think I was perhaps a little over cautious the first time around. Even without Christmas I think I'd have told my best mate and my sister.
With my first pregnancy I was waiting to tell my best friend along with my other friends...not really sure why. I regret not telling her as I had a miscarriage and told her immediately about that so may as well have shared the good news with her as well as the bad. When she got pregnant she told me as soon as she could, which was around 9 weeks (I was abroad until then), before our other friends. I was really touched.