iOS 5.1 Beta 1 was just seeded to developers by Apple. This means if you have a developer's account, you can now download the first beta of iOS 5.1. However, there aren't any new features found yet other than some bug fixes listed by Apple. As the days go on, more secrets of iOS 5.1 will be discovered. Remember, if you are planning to Jailbreak iOS 5.0, DO NOT UPDATE to iOS 5.1 unless you want it tethered.
Let us know in the comments section if you find anything new!