Google Docs is the Best

Couple reasons why I like Google Docs:

1. Imports MS Word, Powerpoint, and Excel format files, PDFs and many other formats as well. (No MS Office 2007+ compatibility yet)
2. E-mail interface for browsing documents.
3. No folder hierarchy to documents. (My favorite feature. Documents shouldn't be stuck to one category)
4. You can enable offline use by installing Google Gears.
5. The best feature of any product: It's free!