I am off to Vegas to moderate a panel discussion on Virtual Office. Unfortunately, the discussion will really be about Hosted VoIP, not Office 2.0. Office 2.0 is the concept of the Virtual Office. At IT Redux, they have pushed the concept to the edge. In their rules for Office 2.0, software apps can only load in a web browser. And files must be stored online. That way you can work anywhere. Access "your hard drive" anywhere. (I would suggest that sensitive files be saved on a 4GB flash drive that can be carried with you. It certainly solves the synchronization problem many people face. This concept is not quite there yet. (Even with Google pushing hard).
The drawback is control. Who controls the access? How good is the security? What if these apps (webistes or companies) are bought out or close? What happens to your data then? What about privacy breaches? If they are free, they will be ad supported and that usually means targeted, so how private is your stored data or online activities?
IT Redux has a pretty thorough list of Web 2.0 apps that can be used to create the Virtual Office space.
I have a small list here.