I tell very few people, including a lot of my friends. Most people (coworkers, friends) don't know. The friends who do know were there 8 years ago when I went into the hospital. I find that its a very personal thing that people don't need to know since they tend to judge. I don't ask about their personal health issues, so why should they know about mine?!?
I also read somewhere a while ago that you shouldn't tell your employer because they may discriminate against you because you have higher health insurance costs. I don't know if that's true or not, but I've not told any of my employers. I figure I wear the medical alert necklace for reason. If anything horrific happened (knock on wood), the paramedics would see the medical alert and respond accordingly.
When I was living in Spain, I had a "friend" who jumped up at a restaurant, grabbed my hot chocolate out of my hand, and screamed at me "You can't drink that, you're diabetic!" I was mortified. The worst part is that I hadn't actually told her, she had just overheard me telling two other people.
So I tend to be pretty private about it. It's just me and I applaud all of you who are more open about it. But for some reason, I just can't be!