CNet News' Robert Vamosi has tried out the Windows 7 pre-beta Microsoft released at PDC2008, and he has the skinny on some of those changes:

Gone is the Security Center, introduced in Windows XP SP2. Instead, there will be an "Action Center" that incorporates alerts from 10 existing Windows features: Security Center; Problem, Reports, and Solutions; Windows Defender; Windows Update; Diagnostics; Network Access Protection; Backup and Restore; Recovery; and User Account Control. Changes to the User Account Control (UAC) may raise an eyebrow or two. While vastly unpopular in Windows Vista, the dialog boxes that pop up whenever a user tries to install new software, among other reasons, served a purpose. In Windows 7, users can adjust consent prompt behavior using a slider control, if they have administrative privileges. Microsoft says they'll still be protected against malicious software, even if they never see another alert. I'm wondering if that's actually a bad idea: if people never see an alert, they might think nothing bad ever happens to their computer. We lose an element of user education.

Other security features have been tweaked in the current build of the next Windows operating system. Scrollbars were removed in the configuration settings screen, as has the Software Explorer feature, and real-time protection in Windows 7 has been improved to reduce the impact on overall system performance. Windows 7 extends BitLocker drive encryption support to removable storage devices, such as flash memory drives and portable hard drives. This means that users can keep sensitive data on all of their USB storage devices. Biometrics enhancements include easier reader configurations, allowing users to manage the fingerprint data stored on the computer and control how they log on to Windows 7. And System Restore includes a list of programs that will be removed or added, providing users with more information before they choose which restore point to use. Restore points are also available in backups, providing a larger list to choose from, over a longer period of time. Returning from Windows Vista are Kernel Patch Protection, Service Hardening, Data Execution Prevention, Address Space Layout Randomization, and Mandatory Integrity Levels.