Let me introduce you to Google Docs. Its the online document editor, which support Word, Spreadsheet, and Presentation. Its in beta version so expect changes in the future. And please not this is the pre-review. I haven't use all of the feature but this is what I can say about my first impression on Google Docs.
Stability: If you have a stable connection, you don't need to be worried. The only problem I have is since I need to re-login every 10 minutes for my connection, the documents sometimes fail to save the latest version. But they also have the autosave feature so I won't lost that much.
Features: Don't expect the superb feature that you can have in Microsoft Office or iWork. Google Docs only have very basic functions in Document Editing. Currently I am unable to find a way to create formula in Word (which is very crucial to me). Also the shortcuts not work perfectly. Im not sure if thats because I use OS X or not. But the most feature that I like the most is the way they keep your document online. This way, I can manage my document anywhere, anytime, using any platform or any web browser. I really love this feature and I think this is the best idea since it lets multiple user to access one document and significantly decrease syncing process. Imagine your email full of documents that need to be synchronized every day. With online document management (aka cloud processing ;) ), merging process can become easier.
User Interface: It's pretty neat. Simple but elegant. It might not be as good as iWork or Office but its definitely better than OpenOffice.
What Went Right: Free, Simple yet elegant, perfect for basic document editing, online collaboration
What Went Wrong: Stability for troubled connection, while creating document is easy, opening document(which require upload) is not that easy, the least feature I've ever seen
Overall: Its very basic for the moment, I'm not sure because its in its beta version or else. But for a collaborative document editing, its very powerful. If you only needs a basic document editing, give this one a try. But if you are a hardcore document editor, I'm not sure this is your best option.