At TEDxStuttgart, we do rehearsals with our speakers. Some of them are still surprised when we mention it - it's not something conferences usually do (maybe they should?).
Such a rehearsal is pretty simple and informal, actually: Two members of the team meet up with a speaker in their home, office, or a neutral place (we don't have offices ourselves and the venue is usually not available before the event). We set up a camera and let the speaker do his or her talk.
