Death of the Kill Switch
The change in Vista SP1 that has garnered the most publicity is the death of so-called Kill Switch (which Microsoft prefers to call "reduced functionality mode"). Currently (pre-SP1), if you don't activate a retail version of Vista after 30 days, or if you ignore a three-day grace period you're given after making so many hardware changes that Windows is no longer considered valid, your desktop turns black, the Start menu and desktop icons disappear, and you can only copy your data files, but you can't open them. In addition, after you use Internet Explorer for an hour, you're logged off.
In SP1, the Kill Switch in essence becomes a Nudge Switch. You'll be frequently reminded that you need to activate Windows and the desktop background will turn black. Try to change it to another background, and an hour later Windows will turn it black again. In addition, you won't be able to download signed drivers and optional updates via Windows Updates, although you'll still be able to get critical security updates. And you'll still be able to use Vista.
Why should you care about this if you've already validated your copy of Vista? The Kill Switch is part of Microsoft's Windows Genuine Advantage (WGA) validation system, and that system has caused nightmares for people and corporations because of Microsoft glitches. In August 2007, many Vista and XP users found their Windows systems disabled by Microsoft because of a Microsoft WGA server glitch. The Kill Switch went into effect on many machines that had validated their version of Windows, and countless people no longer had access to their PCs. With SP1 and the death of the Kill Switch, that should no longer happen. That alone is reason enough to upgrade.
Tweaking the search
The only other notable visible change in Vista SP1 is the way it allows users to substitute an alternate search tool for the one built into Vista, and removes the Search link from the Start menu.
With SP1, you can use non-Vista party search technology, such as Google Desktop Search, as your default search, by choosing Start --> Default Programs --> Set your default programs.
Also, if you choose Start --> Default Programs --> Associate a file type or protocol with a specific program, you'll see a new entry in the protocol section, called Search. Use it to configure which program opens when you click on a file that uses the Windows Search protocol.
In addition, when you type a search term into the Start menu search box and results appear, the name of the category for the links to additional searches have changed from "See all results" pre-SP1, to "Search Everywhere" in SP1. The "Search the Internet" link, however, remains unchanged.