Next month in London I'm speaking at the Open Group practitioners conference which focuses on "Identity in the Clouds". Note that it's "Identity in the Clouds" rather than "Identity in the Cloud", since one of the key issues for identity in Cloud Computing is to tie disparate identity systems together.
For example, if a local application calls up to a Force.com service, the identity of the client must flow up to the Force.com service. The pivot point which connects the local applications to the Cloud is an XML Gateway . If a user is using a local application, and that application is connecting to a Cloud-based service (e.g. to Amazon's S3 storage service), then that connection must be managed based on the identity of the user, not only based on the client application. The decision should not only be "is this application allowed to put data up into Amazon S3?", but "Is this particular user running this particular application allowed to put this particular data up onto Amazon S3?". This is the level of control which the Vordel XML Gateway Cloud Edition can provide. It becomes especially important if local applications are using other Cloud services from multiple providers (i.e. "identity in the clouds" not just "identity in the cloud").
Here, from the Open Group site, is a picture of clouds over London: