Microsoft has recently made a large investment in FourSquare to secure their data for a future digital assistant service like Cortana.
It is therefore appropriate that they return the favour by updating their lagging windows phone app.
The good news is therefore that the FourSquare app for Windows Phone 8 has indeed been updated to version 126.96.36.199.
Unfortunately there is no changelog, but the main changes appear to be bug fixes and user interface improvements.
Find the app in the Windows Phone Store here.