Windows 7's streamlined UAC.
By default (at least in the build given out at PDC), Windows 7 will show Administrator users many fewer prompts than Vista. No user-initiated action requiring elevation (i.e., changing a setting in Control Panel, creating a folder in a restricted location) will result in a UAC prompt. Instead, the elevation occurs automatically, allowing the action to succeed.
However, if a program
attempts to perform such an action, UAC steps in and displays a prompt. This provides a pretty good balance between annoyance and protection. Furthermore, the UAC prompts no longer black the screen out. Instead, they just appear as regular dialog boxes. Read more at the source