The final 2.0 release of MSN Search Toolbar with Windows Desktop Search is now available for free download. I'm not sure I've ever said this about a product before, but Windows Desktop Search may actually change your life!
Disclaimer: I've never used any other desktop search tool for Windows, including Google Desktop. I use Google all the time for Web search and consider it superior to MSN for that purpose, but I've never been able to get their desktop search tool to install on my PC. I used and really liked the Lookout plug-in for Outlook for several months before I transitioned to the MSN tool.
I've been using the beta of MSN Search Toolbar with Windows Desktop Search since a day or so after its public release, and it's completely changed how I organize email and files on my work computer... basically I don't organize any more! I only move email on a handful of specific topics to personal folders, and files either go on my desktop or the root level of My Documents.
I've long struggled to find the optimal hierarchy for saving email and files, but now I don't have to worry about it because Windows Desktop Search is always available and works very well. And it's great to be able to quickly transition from a desktop search to a Web search with one click - very helpful when I'm searching for images or specs of the latest smartphone.
Now, the product is not perfect. First, it's not as tightly integrated in the OS or applications as the Spotlight feature of Mac OS X Tiger. I'm sure something very similar will appear (next year!) in the Longhorn release of Windows, but it's debatable whether Microsoft will do as well as Apple at getting all the small things that really matter right. Second, you can't save searches for quick re-use later. Third, only in limited instances does it auto-filter search restults as you type (I believe Apple's iTunes was the first widely-used app to offer this).
That said, for what it does offer, MSN Search Toolbar with Windows Desktop Search is an incredible product. I highly recommend it to anyone that uses a Windows PC.