http://gregmckinley.com/cs/blog/archive/2006/06/26/15.aspxHere is a use case for an enrollment process: Scenario X - Error: No Response to enrollment request 1.  The customer clicks the enroll button. 2.  System X sends the enrollment request to System Y, but there is no response. 3.  Theen-USCommunityServer 2.0 (Build: 60217.2664)http://gregmckinley.com/cs/blog/archive/2006/06/26/15.aspx#25Tue, 05 Sep 2006 13:10:54 GMT9f8fffc3-80f6-44ee-b09b-68af0d4418c5:25JackHopefully, it is a rare case where the other system fails to respond.  If there were a "backup" system, such as an email with Tx details is sent instead in the background, then the transaction can complete - and the user would never know there was a problem.  Of course, this is an issue if you require real-time feedback.