I don't know about you guys, but if I try to enter some of the more heavy populated areas (Celestia is especially bad about it) with tons of people battling close to each other...
My computer is literally whimpering from having to animate so much at the same time - not just people and mobs walking around outside of the ring, but also all the graphics of people in other battles!
I would really, really like to see some "low specs" setting that would turn off any advanced graphics outside of your own duel ring - meaning that you wouldn't have to see all the other battlers in the area use their spells (and potentially, EVERYTHING outside of the battle ring, including other mobs and players)