How do you deal with unsolicited parenting advices?

I usually smile like a dumb woman and keep nodding my head. In most cases, they realize I am barely listening, as I also look here and there, and am never able to reply to any of their questions in the conversation (of course I am not listening!!!) ;) but you know what, sometimes, some advice can come in handy, and many times, people actually have only good things in mind when they give such advice, so I don't behave rudely or ask them to stop.