About half of our friends know but are not being kept appraised of every tiniest detail. I've been a little surprised at which people I've told and which people I've refrained from telling when related topics came up, but it hasn't been a problem either way. It's a little strange because none of our close friends are parents or planning to be anytime soon, so this is pretty far removed from their experience. It's kind of lonely.
My brother also is in the "knows but isn't following closely" category. Our parents don't know. In the case of my parents, it's to avoid listening to my dad ranting about not wanting a "bastard" grandchild until the last possible minute.
In the case of MrBecca's parents (and all his relatives and the friends who are "his" not "ours") I've been careful to leave it up to him, and as far as I know he hasn't told anyone. I know he hasn't told his mom because she'd be all over us w/"helpful" advice!
I have two former co-workers I see regularly, who both would like to hear every detail. One of them just started TTC, and I enjoy talking w/her and love the idea of being pregnancy buddies; the only thing that gives me pause is that she's always had textbook cycles and I'm a hormonal freak, so she might get pregnant right away and have her baby while I'm still trying, and that would be hard to handle!! It might be worth it tho to have someone to talk w/IRL who's in the same situation. The other has a toddler and is eager to be my role model and would be good at it in that she's an AP WOHM, but she's fixated on "enriching" her baby by buying a lot of stuff I don't think is necessary, and she's all but trying to talk me into infertility treatments which I really want to avoid if I can, so I don't know.... At this point, I'm keeping both of them posted!
I haven't mentioned it to any current co-workers because I don't want anyone worrying about my commitment to my job until the time comes.