Woke up this morning, and smiled. I'd been dreaming that I was playing D&D with my brother and a couple other dream people. We were running 3E characters, I was playing a Monk. But my brother, who was DMing, was apparently using Classic D&D rules on his side. We were fighting some Rock Baboons. The male dream person disappeared, and the female dream person, who was playing a Dwarf Fighter was doing alright, but my poor Human Monk couldn't hit the broad side of a barn and I was slowly getting pounded to death by the baboons.
I looked at my character sheet for something to save me, and I had something called a scroll of cavarous (?), which I thought would somehow turn the baboons on each other, but I woke up before my initiative came up again.
I've read about some people doing that (mixing 3E characters with a Classic world, not inserting scrolls of cannibalism, although that's a good idea too) before to good effect. It keeps the DM from having to worry about all the fiddly crap of the d20 system, while players get to customize and twink their characters as they see fit.
Saving throws would be the only hard part, I'd think. If you just used the 1st level Save values for the players, and let them roll d20+whichever of the three bonuses is appropriate vs. the DC of whichever of the five classic categories is used might work for the players. But for the monsters, you'd need to calculate bonuses for saves against the DCs of the players' effects.
Otherwise, the combination could work really well.
Maybe I could try it with my group. Alex, who hates Classic would jump at the chance, and Pat has said he really prefers 3E/3.5E. But who am I kidding, I don't really have the time to DM right now. As I said before, if we get back to gaming, I should just really shut up and be a player.