I just got my BFP this AM, will double-check with a digi this evening.
I think "when to tell" is a personal decision. The rate of MC goes way down after 1st tri, so a lot of people wait until then. I believe the rate is also lowered after you hear the HB. However, anything can happen, so I'm not sure that any time is "safe".
The biggest thing for me is waiting until after 1st tri to tell "the world" and to also wait until after that time to tell anyone who may "spill the beans", i.e. my MIL! My plan is to call (probably tomorrow) the OB/GYN that I want to be my Dr. and see when they would want to see me. If it's soon, then I may wait to tell anyone but DH. If it's not until 8-10 weeks (normal), I may not be able to hold out telling my mom and possibly my BF. Also, my BF is on "baby watch" with me and makes me drink some sort of alcohol when she comes home (she lives about 3 hours away). So, if she comes home anytime soon, I'll probably have to spill the beans.
With the timing, April Fool's Day is exactly 14 weeks for me. I may tell anyone that we want to tell in person/via phone the weekend before that and then do a facebook announcement on April Fool's Day - keep everyone guessing!