The OpenOffice.org2GoogleDocs extension imports documents from Google Docs and Spreadsheets to OpenOffice.org and exports from OO.org to GDocs so you can work with your docs both online and offline. Works onWindows/Mac/Linux. Also it is a simple way to backup your local documents to the internet.
The OpenOffice.org2GoogleDocs extension is free, works anywhere you’ve installed OpenOffice.org. Web site DocSyncer is looking to do similar things for your Microsoft Office docs, but right now it’s in an invite-only beta. Needs Java 6 to work.