With DS I told at 5 weeks when my clinic confirmed it. I was in the Air Force and HAD to tell 10 people right away (since I was no longer deploy-able) so at that point my whole office found out and so we told the whole world.
With my second pregnancy we announced after we heard a heart beat at 8 weeks and miscarried at 11. I loved the support and was glad that I could talk about it openly.
This time we waited until 9 weeks because we wanted to tell SIL and my bro in person on our vacation.