I don't think I was ever asked if it was planned, because I'm a lesbian and my wife shared the news on facebook, so asking if it was accidental would imply that I cheated on my wife...but some people get really silent, like they want to ask that, and I just write something like "it's not like it was an accident" so they don't have to ask. I would never ask someone that unless it was a very close person, and the only reason I would do it was to know if I should sound excited for them or not (because I'm instantly excited about anyone that gets pregnant), and I think that most people that ask that do it because of that...still, I really don't think it's their place unless they are your sister or your best friend.
I had, however, some people really really nagging me about having a Christmas baby. One of them actually kept on and on about how the child will be traumatized. I tried to take it as a joke, but he (yes! he!!!!) went on and on about how that would never happen to him, and how he doesn't understand why people can't just skip one month. I told him something like "well if that's your line of thinking, you'd have to skip at least 4 months...you never know if you're going to get a preemie or if the child will take longer than expected to be born.", but I got really annoyed at him, specially because he had this argument on my facebook announcement post.