Okay, I've got Diplomacy maxed out and am finding myself a wee bit frustrated by how many dark side missions there are as opposed to light side (on my Jedi Shadow), as when missions result in dark side point accumulation, my character takes a fairly substantial hit to endurance / hit points (to the tune of more than 1,000 hit points), and this affects my ability to play.
When this happens, I have to try and only do light side missions to get my light side points back up, but sometimes they are not even available, and so I have to go further into dark side corruption to get the light side missions to show up on the list. For instance, right now my character is 144 on the dark side, and only two missions are available for 30 points each on the light side, so it will be some time before I am able to get my hit points back.
I'm not sure what else dark side corruption affects character wise, but my character is noticeably weaker as a result, and it seems to me that the effect of dark side corruption on a light side character should be lessened or manifested in a way that does not interfere with actual gameplay.