Foursquare screenshots from iTunes
According to Mary Beth Quirk, writing at The Consumerist, the two key paragraphs in the email are:
1. We will now display your full name. Currently, Foursquare sometimes shows your full name and sometimes shows your first name and last initial (“John Smith” vs. “John S.”). For instance, if you search for a friend in Foursquare, we show their full name in the results, but when you click through to their profile page you don’t see their last name. In the original versions of Foursquare, these distinctions made sense. But we get emails every day saying that it’s now confusing. So, with this change, full names are going to be public. As always, you can alter your ‘full name’ on Foursquare at https://foursquare.com/settings.
2. A business on Foursquare will be able to see more of their recent customers. Currently, a business using Foursquare (like your corner coffee shop) can see the customers who have checked in in the last three hours (in addition to the most recent and their most loyal visitors). This is great for helping store owners identify their customers and give them more personal service or offers. But a lot of businesses only have time to log in at the end of the day to look at it. So, with this change, we’re going to be showing them more of those recent check-ins, instead of just three hours worth. As always, if you’d prefer not to permit businesses to see when you check into their locations going forward, you can uncheck the box under ‘Location Information’ at https://foursquare.com/settings/privacy.
You can find more information about these and other changes at Foursquare in their Privacy 101 statement. This page includes information about how to remove your home address from being shared and who Foursquare is sharing your information with including brands and third-party apps such as Facebook.
The new privacy page is Foursquare's attempt to communicate in plain language exactly what they do with your information. Lessons learned from Facebook and Instagram showing that legalese privacy statements don't make users happy, perhaps? Also, lessons learned from others may have prompted Foursquare to be completely upfront about how to opt out of anything you are not comfortable sharing.
The changes don't go into effect until January 28, so you have a few weeks to figure out if you want to make any changes in your settings. You can opt out of revealing your full name or of letting businesses see your location information, or both.