What are your personal preferences when it comes to mapping the keys?

Here's mine:

right click - action
E - spells
Q - equip/unequip weapons
tab - inventory
F - auto run
X - crouch
R - rest
T - journal
spacebar - jump
shift - toggle run/walk

The rest should be the default keys, like attacking should be left click. This is pretty much the same keyboard layout I use for every other games, except that I just recently switched action with spells. Other wise, the E key is usually my hotkey for action for all my other games.

Default, because I am lazy.

I get the same feeling when I have to remap the keys, but thankfully, I have it set up in my mind, which makes it less of a pain.

right click - draw weapon
left click - use/attack
c - cast spells (I use a mod that casts spells without having to "ready magic")
shift - run/walk
crtl - sneak
e - jump
space - activate
tab - inventory

left click - attack
right click - use
mouse side button 1 - move forward
mouse side button 1 - move backward
mouse top/central button - sneak

many mouse buttons = ideal for chain smokers

All default, except for the sneak key which was a bit too far on the left for my tastes. So "Left Alt" it went.

Default, but I switched the action and jump buttons.

Me too.

Morrowind uses the standard PC movement "W,A,S,D" layout, which I like. Changing them would be too confusing.

Default for me too. I don't remember having a problem with Morrowind's default layout.

Left click = attack.
Right click = nothing.
Q = use.
E = cast spell.
R = draw weapon.
T = rest.
C = change view.
Spacebar = jump.
Tab = menu.
Shift = sneak.
Num Lock = autorun.
Forward slash = toggle running/walking.
Ctrl = run/walk.
J = journal.

And I can't remember anything more. Just typing this from one of the computers at my college, don't have access to the game ATM.

I only switched the first person/third person toggle and the inventory button around, oblivion style. So middle mouse button to check out my character, tab to open inventory.