Apple released a 3rd beta build for iOS 4.2 on Tuesday, along with a 2nd for iTunes 10.1. It looks as though new builds are coming at roughly two week intervals at this point.
Developers Get New Betas for iOS 4.2, iTunes 10.1

Apple released a 3rd beta build for iOS 4.2 on Tuesday, along with a 2nd for iTunes 10.1. It looks as though new builds are coming at roughly two week intervals at this point.
Along with the arrival of sexy new iPod Touches replete with pixel-packed Retina Displays, touch-capable iPod Nanos and rollback Shuffles, today should see the debut of iOS 4.1 as well as Apple’s new iOS gaming social network, Game Center.
As such, TUAW is reporting that Game Center has just gone live for iPhone developers, meaning that instead of being limited to a sandbox-only development environment, Game Center is now allowing global registry and asking for new login details… older accounts having been purged from the system yesterday.
Game Center’s reportedly having a few birthing paints, including some crashing issues and connectivity problems, but it seems to mostly be due to server problems, and everything’s working once you manage to get connected.
Since Game Center is the showcase new functionality in iOS 4.1, the server switch being flipped on is a good indication that we’re all about to see an update get slurped down through iTunes sometime soon.