According to Foursquare, the key changes - which will come into effect on January 28 2013 - are to how accessible your data is, both publicly visible and to businesses you check into. Whereas currently a mixture of full names and first names and last initials are used, the new default will be to show first and last names consistently; that, the company says, is to address complaints that the existing approach is "confusing" and makes finding the right person in search results tricky.
As for businesses, the amount of data they see on each customer will not change, but they will get data for a longer period. Currently, Foursquare shows check-in activity for the most recent three hour period; that's being increased to cater to those businesses who might sift through the results less frequently than that:
"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" Foursquare
Wary of a sharing backlash, Foursquare is eager to highlight what privacy settings and options users have to play with. Although the company will soon show full names by default, it only requires a first name for registration; you can change what your "full name" is in the settings.
Meanwhile, there's an option in the "Location Information" section which allows users to turn off the ability of businesses to see when they check into their locations. There are also Private Check-Ins, which hide the data from everyone, including both friends and businesses on an ad-hoc basis.