I doubt any of you care to hear it, but I want to voice the idea to get it out of my head.
Basically, from what I've read, people keep suggesting a central way for all worlds to use magic. Keeping in line with what I've seen as the desire to let players customize what they want their world to be like, this sorta rubs me the wrong way...
My idea is this: Make up a collection of 'rules'. When generating a new world, players are given the option of either randomly letting them be selected, or going through the list and specifically choosing what they want magic to be like. 'No Special Effects', for example, could mean that you won't see any fireballs or lightning bolts flying through the air.
This can let players pick and choose exactly what kind of flavor they want: If they want a world like Middle-Earth, where people who can use magic are like Gandalf, then they can set it up that way.
If they want a world where everyone and their little cousin has at least one little trick that they can pull, then that's also doable.
It'd be a chore to code, I'm sure, but I have to voice the idea at any rate...