It's a familiar problem: you're heading to an unfamiliar city and looking for things to do, but you'd rather not ask each and every friend in the area for advice. What do you turn to? Foursquare has an answer: it just launched Trip Tips. The site lets you give friends a custom link where they can suggest places to go based on where you're traveling and your own notes. Any locations they offer will go into a Foursquare list that you can use to plan your itinerary, whether it's on the web or in mobile apps. Your friends can even save the list for themselves, in case there's something they hadn't already tried.