I was a blabbing fool as soon as I found out! I told my two childood BFFs, my closest adult friend, and my mom the day I found out. DH told his parents the same day (despite having just had dental work done and slurring his way through the conversation). The next day I broadcasted it on Facebook so most of my extended network found out.
I got my BFP on spring break, when I went back to work Monday I told a coworker who knew we were hoping and trying, but she's the only person who knows at work.
I haven't told my dad because he's a negative jerk. I don't know when I'll tell him.
The person I want to tell most, though, is DS. He's going to be thrilled! He was asking me just the day before my BFP if he'd ever be a big brother.

I'm waiting 'til late June, just in case... DH and I would be very upset if something happened to this baby, but I know we'd ultimately understand and recover (I had a m/c in '03, I know this for a fact with me, I was surprisingly peaceful). DS, however, would probably carry that with him for the rest of his life, he's a very sensitive soul.
And I'll probably broadcast it at the end of the school year (late June), though I anticipate people (especially students!) will be guessing by then if my snug pants are indicative!