One of my favourite Google applications is Google Docs. Its still in beta but it works just fine and haven’t had any bad experiences with it.
I use it to share documents and collaborate information. Great for To Do lists, Planning Projects/Vacations, Organisations and general business use.
The best thing about it is you can create documents online and work on the document at the same time with any user with an internet connection. If both people update the same data it prompt you to resolve the conflict with no data loss. You can create Spreadsheets, Documents and Presentations. (I was deliberate not to mention any of the Microsoft office products as these work quite differently!!).
You can Import and Export documents to and from your Google account and this works okay however if you have word documents with tables and special formatting you might need to work on it after importing.
An amazing tool Google, great job.