It seems like the leaked details of the release of iOS 4.1 as seen in Apple UK website went as planned.
iOS 4.1 update contains several improvements and bug fixes, including fixes for proximity sensor issue and other flaws.
Before downloading the latest update, make sure to back up your data first. You’ll need to connect your device to your computer’s USB port, and then hit iTunes. Under the device menu, select your iPhone or iPod Touch and click “Check for Update”, and follow the on-screen instructions to install the update. You can also get iOS 4.1 on this direct download link.