Hardly anyone mentions the need for a CPE which IMHO is a requirement for a cloud computing model. Today MSFT announced that their next version of Office will have a free online version. But one of the big features of a cloud is "offline browsing/applications". That is the only way to protect oneself from highly publicized outages at Amazon a few months ago and Rackable a few weeks ago.
CPE that enforces local security policies including authentication & filtering. Offline browsing and metering is a business model requirement in cloud computing.
The other function that is hardly discussed in CC discussions is syndication. I have been trying to add an animation/3D module to Google's online presentation (powerpoint equivalent), but not even google has open plug-in architecture to enable this. Unless folks think that Cloud is just another proprietary application running on the network, this functionality is the key extensibility requirement for a useful CC app.