10. A system for differential dynamic content delivery, the system comprising a computer processing unit, a computer memory operatively coupled to the computer processing unit, the computer memory having disposed within it computer program instructions capable of: providing a session document for a presentation, wherein the session document includes a session grammar and a session structured document; selecting from the session structured document a classified structural element bearing a preview designation; providing a preview of the selected structural element to a prospective user participant; receiving from the prospective user participant an indication of interest in the selected structural element; and recording the presentation for the prospective user participant based on said indication of interest and on the prospective user participant not attending a presentation session.
10. A system for differential dynamic content delivery, the system comprising a computer processing unit, a computer memory operatively coupled to the computer processing unit, the computer memory having disposed within it computer program instructions capable of: providing a session document for a presentation, wherein the session document includes a session grammar and a session structured document; selecting from the session structured document a classified structural element bearing a preview designation; providing a preview of the selected structural element to a prospective user participant; receiving from the prospective user participant an indication of interest in the selected structural element; and recording the presentation for the prospective user participant based on said indication of interest and on the prospective user participant not attending a presentation session. 17. The system of claim 10 , wherein a plurality of user participants includes the prospective user participant, a first user participant and a second user participant, the system further comprising: presenting during the presentation session a first version of the presentation to the first user participant and a second version of the presentation to a second user participant based on differences in user classifications between the first user participant and the second user participant.