alt Hacker NewsI often tend to integrate talking passionately about a topic in my head with an imaginary interlocutor. While not directly being a rehearsal in itself, it really helps with developing ideas and chaining concepts - at least for me.
I guess everyone is different in regards to handling the pressure when talking in public, but I do agree that you can feel it, most of the time, when someone rehearsed too "scholarly".
On the one hand, I tend to not do formal rehearsals a lot of the time. On the other, I also find that if I give a live talk for the second or third time, it often is better because I find some things that worked in my head don't work as well on stage.
All that said, an overly-rehearsed talk can come across as stilted/reading from a script.