If you have not already discovered Google Apps, and prefer using Microsoft Word applications, you should try the plugin for Microsoft Office, called Docverse.  This instantly turns your Microsoft Office applications for Word, Excel & PowerPoint, into an office collaboration tool.  

The plugin works similar to Google Docs, and allows you to collaborate on documents with your colleagues. Updates and edits made by your colleagues can be seen  in real time.  Also, a version of your file is stored on the Docverse cloud server, so you can access your files when your on the run.  

Here is an example of how Docverse integrates with your PowerPoint...

As you can see, you can easily add additional editors, leave comments, receive updates when your shared document is updated, and keep multiple versions of your Word, Excel, or PowerPoint file in sync with Docverse online.

For single user access, Docverse provides you with a free account, which could be ideal to keep your office files synced with an online version.  If you want to start collaborating with colleagues, then you will probably need their team edition, which is $49/month.  This lets you collaborate on 500 documents, with up to 10 users.  They also offer a 60 day free trial.