Ah, good another few kindred spirits who agree with me. Aye, get rid of the whole foul institution of magical differentiation. If you want to have magic work in different ways in your setting, the rules should let you, but they shouldn't force you.
In my world, I let sorcerers and wizards learn any spell from any spell list. Have clerics or druids suffered? No, they have not, because of just a few little things:
Clerics: better BAB than wizards and sorcerers, better hit dice, better saves, a few more class abilities, and, by the core rules, ability to wear armor (I also let my sorcerers and wizards cast in armor, though they are not proficient in it).
Druids: better BAB than wizards and sorcerers, better hit dice, better saves, a few more class abilities, and more skill points.
So yeah, it makes sense to me that Druids and Clerics should have a more limited spell list than the 'pure' spellcasters. I find it perfectly balanced, and it doesn't force parties to have to have a cleric to survive.
I'm also considering adding in the Hit Point/Wound Point system, so people will heal Hit Point damage at an hourly rate, thus negating any real need for healing most of the time. I really don't like the concept of clerics and druids, so I want to phase them out.
Rather, I like multiclassing. I will use Fighter, Expert, and Magus as my three classes. Fighters are unchanged, being the combat class. Experts will basically be the skill-monkeys who get all kinds of skills, but few other abilities. Magi will be the magic class.
If you want to be a cleric, you take equal levels of Magus and Fighter. If you want to be a rogue, you take a few levels of Fighter and the rest of Expert. If you want to be a bard, take some levels of Expert, Fighter, and Magus. And so on.
As far as I can tell, the arcane-divine division is just a sacred cow, which we can easily put out to pasture. If people want it, it will be there for them to use, but they don't have to. If you want there to be a difference between magic from the gods and the magic from the world, implement it in society, so that followers of certain gods aren't supposed to learn certain spells. You don't have to enforce it mechanically, though.
D&D is defined by having classes, levels, dungeons, and dragons. And the last two are optional. As many have said before, the system you use really doesn't matter too much, as long as it doesn't complicate things. A system is there to make the game flow quickly and enjoyably. The current arcane-divine distinction is an unnecessary barrier against some types of originality, and thus it isn't helping the game. I say get rid of it, or just move it to a sidebar as an optional rule.
Mind you, I'm still trying to find a way to make one spellcasting class that mixes wizard and sorcerer. I posted my Magus class in the House Rules forum, but the first draft was pretty complicated. I think I might just scrap the whole spontaneous/prepared designation too. Spellcasters still must acquire spells, but once they learn them, they can cast them freely and spontaneously. I think I like that.