While I'm glad Pathfinder is out there, slowly but steadily becoming the Galactica of the OGL Fleet, the more I read the discussed changes, the more it's looking to exacerbate the problems I had with 3e, rather than solve them, to the point where a character would be too complicated to play after 4th or 5th level or so, with the boatloads of extra feats and class abilities, the extra racial bonuses, etc. What's more, a monster more complex than the ones in 3.5 would be impossible to run for me.
I think there is just a fundamental difference between what people like in game. 3E has become to intricate and complicated for my taste, and 4E is the fix for me. But there are definitely people that like having several subsystems to master with each class. Pathfinder exemplifies this with the new subsystems for Rage, Domains, Spell Schools and Sorcerer Bloodlines.
It is a different kind of "exception based design". 4E is full of small, contained exceptions. 3E and Pathfinder contain "big exceptions" in form of sub-systems. They are barely comparable to each other and you need to learn each subsystem mini-game.
From a game design point of view, I think the mini-game/subsystem method for different classes is what makes it so hard - or impossible? - to balance them correctly. You introduce very different mathematic approaches to the same conceptual area of the game - combat.
But then, each class can give you its own "mini-game" of resource management and abilities. That's the attraction. The difference between two classes and two characters is not just some numbers, the mathematical formula behind it are different, too.
Ultimately, I just don't like the latter approach that much. You have to relearn a lot for each character you want to create (unless you focus on one class - not that uncommon, either). The balance is weak, and you end up with a lot of complicated aspects.
My Savage Tides DM converted his game to 4E (after a brief Pathfinder experiment). We converted from 11th level 3E to 15th level 4E character (since he wanted the campaign to end at epic level). He created and converted a few monster, which was very easy, as he professed. He had no real idea what characters at level 15 could pull of, what their numbers would be (attack? hit points? damage? defense), and it just worked seamlessly. He didn't have to read through half a page of NPC tactics to make the NPC work effectively. And there can be no doubt that every one at the table still had fun and was challenged.
I can't imagine jumping into a 15th level 3E D&D game with that ease.
And regardless of what complaints people can bring up against 4E, the ease of play and the game flow is just so much more enjoyable so far that we just don't like going back.
Which, for the record, we did yesterday - A Pathfinder adventure path with Pathfinder Alpha 3 rules. Well, it worked, but... Something was missing. The combat just didn't feel that interesting to us. And when my Paladin made it to level 2 and we read through the Paladins Lay on Hands ability, we wondered what use it would have in combat (none?) or out of combat (Wand of Cure Light Wounds, anyone?) and how much nicer Healing Surges and 4E Lay on Hands works by contrast...
Edit: maybe I come down a little to negative on Lay on Hands, but I think it exemplifies the whole mini-game thing for 3E that I just don't like anymore:
Usable once per 2 Levels+Charisma BOnus, heals (Level) Hit Points. I was just underwhelmed - to figure out the effectiveness, my 3E experience was helpful - I am not sure beginners would have find it that easy. Healing my level in damage is at no point useful in 3E Combat if it costs you a Standard Action!
Such a complicated way to express an ability that is not very useful in the end!