I enjoyed your Django and OpenID talks at Webstock in 2008 - they fit the conference and audience perfectly. However Webstock is a 400 person conference hosted in a remote part of the world. I'm not convinced that the niche of conferences that want speakers for such technical topics is large enough to support an agency you described.
I'm not so interested in an agency for conferences, since most of the conferences I speak at can't afford to pay their speakers (or if they can, don't pay them enough to make it worth having an agency involved). I'm interested in an agency that gets bookings for private talks at companies - really sort of one day consulting gigs.
In my case, I'd give a talk at a conference like Webstock and note at the end (probably just in text on a slide, no need to say anything out loud) that I'm available for internal talks at private companies. If anyone in the audience asked me about this afterwards I'd put them in touch with the agency. The agency negotiates pricing / travel / etc, and also actively sells my talks in other media (taking out adverts in "CTO Monthly" promoting the 20 or so speakers and topics in their stable).
I'm pretty confident that the niche of companies that want to engage technical experts for a combination of tech talk + a day consulting in the office is big enough to support something like this. I just have no interest in doing it personally - the reason I want it to exist is so I don't have to negotiate / market / coordinate the above points myself.
