Am I embarrassed to admit I was a JW? Depends on who it is and how they might react.
I once had a girlfriend freak-out and practically start hyperventilating. I did all I could to assure her I wasn't one anymore.
I think in certain circumstances, where I want to present myself in the best possible light, I would definately NOT bring it up. We all have those political situations where you try to keep to neutral conversations. Mostly, I'm thinking of people like bosses or VP's that might affect my future career. My judgement and reputation must stay in high regard.
Many people see the JWs as a cult and an annoying one at that. To admit I was a part of that may ruin first-impressions before I get a chance to explain my current standing - and make me look like a fool for once following them. Or, on the other hand, if I start bad-mouthing the whole thing, and the person IS a JW, is studying with them, or maybe has relatives that are JWs and is sympathetic to them, I ruin the impression too.
On the other hand, with most people, I don't hesitate. To use the old JW lingo, I think it's "a good witness" to people. Many people have questions about the JWs, but are afraid to ask. Knowing you're an ex-JW, they often feel free to ask about them without fear of offending you by asking questions like "why don't you guys celebrate this or that"? It gives me the chance to set them straight and help them avoid getting involved.