Couple Things

[Darkened Skies]

I really like that idea too. It gives people completely different options that aren't really currently viable. I've known characters who are essentially pacifists that have been around for years and never reached max level.

[Thief Of Navarre]

Rogues get xp for locks (so you cant take a cross class dip).
Priests get xp for healing 'damage' e.t.c.
Warriors get xp for intercepts and sheilding others!

[Twisted-Indoctrine]

Mages get xp for rendering benches invisible.

[Kangleton]

Mages get xp for rendering benches invisible.

Yes plox. I would farm the Second Wind Inn for XP like it should be.

But this is all very tricky. Not all priests heal, not all priests preach, not all priests smite. Not all rogues open locks, not all rogues pick pockets, not all rogues hide. Etcetera. You can't assign it by class and skill, or you'll only provide for stereotypes.

It's also easy to heal people - you can do it infinitely, really. But you have limited crafting ability. There are limited locks to pick. There are only so many opportunities to make swim/jump/climb checks. Doing it by skill seems like it'd be pretty limiting.

This is why I suggested a catch-all no XP for monsters, extra XP for time spent RPing sort of deal. It would be expected that the time spent RPing would at least make reference to the activities the character should be performing. And, if not, DM smite. Easier to punish the wrongdoer in a system that caters to everyone as a group, than to make a system that somehow simultaneously caters to everyone as individuals, all the time, without room for exploitation.