In the book Yoda Dark Rendezvous, A Clone Wars Novel, by Sean Stewart, Count Dooku actually does attempt to turn Yoda to the dark side. Whether intentional or not Yoda reveals a 'dark side' to himself and Dooku realises that if Yoda was ever to turn to the dark side Sidious would be annihilated.
I personally believe that Yoda didn't turn to the dark side when confronting Sidious, although this may give another reason why after fleeing Yoda exiled himself in disgrace. I was under the impression also that Yoda was merely stopping the lightning and then forcing it back at its creator. This may be why Sidious was surprised, because Yoda was able to force the lightning back at him with such strangth.
Another note towards Luke choking the guards is that at the time ROTJ was created force powers hadn't yet been divided to 'light' and 'dark' sides. Also, Luke hadn't had proper jedi training so may have just been using the force to his benefit, not thinking that some actions may have been considered 'dark'.