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.
Windows 7 build 6801 unveiled at PDC2008, also introduces something called the Windows Filtering Platform (WFP). The idea is that third parties can take advantage of aspects of the Microsoft Windows Firewall in their own products. Microsoft says "third-party products also can selectively turn parts of the Windows Firewall on or off, enabling you to choose which software firewall you want to use and have it coexist with Windows Firewall."