Everyone knows about Facebook and Twitter, and many know about Google+. But do you know about Foursquare?
Foursquare is a newish social network based on geolocalization, that is, finding out where people and places are on the Internet based on their location. Example: you're in Venice at the Accademia Museum and you want to know where nearby restaurants are. Or you're in Milan for a day and want to see where people you know are (only possible if they're on Foursquare). I checked under the search term "restaurants" in Padova, the town I know best, and found a long list, but without much other info besides type and contact info. There are some "tips" (micro-reviews) but they were relatively few and they were in Italian. So, at this point, this is best used in conjunction with other sites i.e. find the places near you and get more info by googling the name you've found.
You can register at Foursquare on your computer and explore it, but it is optimally used on a smartphone, for obvious reasons of mobility. Check it out here.