I told a few close people exactly why I stopped drinking. For others I waited until more recently (8 months sober) to tell them and I word it as "I haven't drank since December". I have never gotten a judgmental response to this statement. Everybody's been impressed by my sober streak actually - "Wow, no alcohol since December?! That's awesome." It's almost said as if they wish they could put it down too.
I remember one time I must have looked a little ashamed and my friend said "Well don't look so down about it. That's a really good decision. You should be happy".