New Home screen tips widget assists new users on how to configure the home screen with shortcuts and widgets and how to make use of multiple home screens.
The Phone, applications Launcher, and Browser now have dedicated shortcuts on the Home screen, making it easy to access them from any of the 5 home screen panels.
Improved security with the addition of numeric pin or alpha-numeric password options to unlock device. Exchange administrators can enforce password policy across devices.
Remote wipe: Exchange administrators can remotely reset the device to factory defaults to secure data in case device is lost or stolen.
Exchange Calendars are now supported in the Calendar application.
Auto-discovery: you just need to know your user-name and password to easily set up and sync an Exchange account (available for Exchange 2007 and higher).
Global Address Lists look-up is now available in the Email application, enabling users to auto-complete recipient names from the directory.
Camera and Gallery
Gallery allows you to peek into picture stacks using a zoom gesture.
Camera onscreen buttons provide easy access to a new UI for controling zoom, flash, white balance, geo-tagging, focus and exposure. Camcorder also provides an easy way to set video size/quality for MMS and YouTube.
With the LED flash now enabled for the Camcorder, videos can be shot at night or in low light settings.
Certain devices like the Nexus One can be turned into a portable Wi-Fi hotspot that can be shared with up to 8 devices.
You can use your Android-powered phone as a 3G connection for a Windows or Linux laptop by connecting their phone to the computer with a USB cable. The connection is then shared between the two devices.
Multiple keyboard languages
Multi-lingual users can add multiple languages to the keyboard and switch between multiple Latin-based input languages by swiping across the space bar. This changes the keys as well as the auto-suggest dictionary.
Dalvik Performance Boost: 2x-5x performance speedup for CPU-heavy code over Android 2.1 with Dalvik JIT.
The graph to the right shows the performance speedup from Android 2.1 to Android 2.2 using various benchmark tests. For example, LinPack is now more than 5 times faster.
Kernel Memory Management Boost: Improved memory reclaim by up to 20x, which results in faster app switching and smoother performance on memory-constrained devices.
Soure : Developer.android.com