My two biggest concerns with a potential third trilogy are plot continuity and quality.
I really don’t think these episodes should be produced, but that might just be because Eps. 1 and 3 were good but not great, and episode 2 was the worst yet. (Judging by this, we probably will never again have Star Wars movies as good as Eps. 4, 5, and 6).
I also remember reading leaked plot scripts for these episodes on SuperShadow a while back. While these weren’t necessarily authentic, they essentially destroyed the idea we have of the SW Expanded Universe that has been developed through comics, novels, and guides to Star Wars (including the official encyclopedia). My worry with regard to additional star wars films is that this expanded Universe will be largely ignored (in addition to the fact that they probably won’t even come close to doing the original trilogy justice), especially if upcoming Lucasarts games like Force Unleashed are any indicator of where the franchise is going.
That said, I think Force Unleashed will be a really cool game, and I’m really anxious to hear more about the planned SW live action tv program, which will hopefully develop more of the secondary characters from the movies.