With Google (JotSpot), Microsoft (Office Live) and others working on deliver some notion of Office 2.0, Ramana Rao, formerly of Xerox PARC, posted his list of barriers to Office 2.0 adoption:
Data Ownership and Privacy
Ease of Migration
Fragility of Aggregated Services
Jason Wood adds two more, scalability and service entitlement and provisioning. The eight issues offers a useful way to gauge the ripeness of the services promising productivity nirvana from the cloud.