(Note: Some of the homebrew utilities mentioned below are unsupported and/or still in their beta-testing stage. I've used them all successfully, but proceed at your own risk.)
User Account Control
Vista's most vilified feature, , will be a little less obnoxious in Windows 7: You can choose from four security levels that dictate how often UAC will bug you. , a free (and "experimental") download from Symantec's Norton Labs, extends similar courtesies to Vista users, replacing the stock UAC with a version that delivers fewer duplicate intrusions, a 'Don't Ask Me Again' option, and useful details about the nature of the security alert. Alternatively, check out , a system tray utility that puts Vista's UAC to sleep for a designated period of time--helpful if you're planning to do some system tweaking and you don't want to be bothered every step of the way.
The Taskbar
Windows 7 has drawn raves for its overhauled taskbar, which sports big, inviting icons and lets you "pin" frequently used applications and documents. Well, guess what: You can get an almost identical taskbar in Vista with just a few clicks.