Nice comparison by ReadWriteWeb. I wish they had included Zoho also.
Sarah Perez / ReadWriteWeb:
Office Live Workspace vs Google Docs: Feature-by-Feature Comparison — Today, Microsoft announced that the Office Live Workspace beta is publicly available for everyone to access. The site, a free web-based extension of Microsoft Office, lets you access your documents online and share your work with others.
Lifehacker has a comparison of Google Docs and Zoho.