Foursquare has just rolled out version 1.9.0 for iPhone and iPod touch which brings iOS 4 and iPhone 4 support.
This new version brings a new map view where you can see all your friends, high-res graphics which are optimized for iPhone 4 Retina Display, performance improvements and bug fixes.
The official change log is as follows.
* View your friends on a map
* High resolution artwork for the iPhone 4 Retina Display
* Performance improvements and bug fixes
Unfortunately, the support for iPad is still missing. Also, the app doesn’t take advantage of background-ing feature of iOS 4, what this means is that we cant update location in the background. However the version 2.0 of the app (which is already in the works) will hopefully be a significant change and will take advantage of all the new features of iOS 4.