I've been a user of Google's free Docs & Spreadsheets software for about 6 months. In fact, that's how I wrote this blog. Sure, I am giving up a few things, like true drag-and-drop capabilities between file folders, and using the software means I have to be tethered to an Internet connection. But honestly, how often does one work without an Internet connection these days?
In order to blog, I need access to sources, e-mail, RSS feeds, etc. I can't really write without the Internet, so it's not a big deal for me to always be connected. Plus, if I ever travel anywhere, I always know that my documents will be available to me through the Internet. I never have to worry about transferring files from one machine to another. Lastly, if you need to have compatibility with other document programs, Google's software allows you to save documents as Word or Excel files, which will natively open in Word or Excel.
For mobile workers constantly on the go, having the right files with you is often half the battle. And for this self-employed freelancer, Google's free version of Docs & Spreadsheets has saved me a bundle. We'll have to wait and see how the $50 version appeals to the corporate masses.