When I transitioned i chose to be public and open about it. I figured there was no point in pretending otherwise. Just changed my name and gender marker in FB and made a general announcement. Got great support, but then I only have direct friends and colleagues as FB friends anyway. I came out at work, got great support, but I had great open minded colleagues. I had a bit of a profile through work with the wider sector, so I put a small article about my transition in the company newsletter - that way I could be relaxed and open about it, rather than awkward, if I met up with others who had known me later. That actually worked a treat, the amount of support I received was awesome. Told the readers of my webcomic in a public announcement, got the most comments to any post I'd ever made, over 100... all of them positive and supportive. But now all the outing is over, I'm just getting on with my life as Grace. I'm not trying to be stealth but neither am I wearing being trans like a big neon sign... I'm just being Grace.
I guess a lot of it depends on the people you know, associate with, have a history with. If they are closed minded haters, I guess I'd be not bothering to tell them. Chances are they'd find out anyway - the "OMG did you hear that X is now a woman" grapevine catches fire with the slightest spark, believe me. If your friends, etc are open minded and progressive then maybe there's no issue. It is a tough call.