Great points. Some people ask these questions on purpose. Others, because they really don't realize what they are getting themselves and others into.

To find out what a person's intentions are, follow up their question with a question? For instance

What do you think of Bob's new girlfriend?

Why are you asking? Is there something about her I should know about?

There is nothing wrong with asking a question about a question if it is to get more information. It not only prepares you for your answer, but it gives you an idea where the conversation is headed. You can then decide to participate or punt. like "I really don't know her well enough to comment". And then go to another topic you are more comfortable with.