I would love the ability to have multiple custom key mappings (and it seems like it would resolve a few suggestions already made by others). I know about 2 years ago the only way to do this was by copying and renaming a file (something like keymap.ddo, I think, renamed to keymap1.ddo, or whatever), but each time you wanted to switch them out you had to quit the game, change the names around again, and start the game back up.
I realize it would be a bit redundant to have a different key mapping for each toon, but maybe let us have 3 different custom key mappings we could save? I always want this when I go from playing my rogue to any kind of caster/healer, as suddenly it is a lot more important to be able to target party members or find spells instead of going into sneak mode or changing weapon sets. It seems like the whole way one interacts with the keys/controls differs greatly depending on your build, and it would be nice to have an easy way to switch things up ....