I never mentioned it, and I left it to them to manage their own reactions, which they politely did without bringing it up to me. 🙂 Well, except my one dorky college friend who got all flustered and left a "nice tits! how weird." on my FB, and I ignored it...
I guess it never occurred to me to talk about it, and I didn't have much of a window before I didn't *need* to actually say it, either - I ended up coming out at work early before I was outed by being 42C at three months HRT. I *did* make a point of wearing outfits that downplayed them around my parents for a year or so, though, to give them time to adjust.