My games are continuing as 3e. I may adopt some individual things from Pathfinder and 4e but essentially it will still be houseruled 3e.
Individual bits like diagonal movement and charging are elements that I've heard good things about and could easily be houseruled into 3e. Zombies popping up after dying sounds good too.
The no online srd rules for 4e though makes running a pbp game in 3e much more atractive looking right now.
4e would have to be spectacularly easy to learn, DM, run during a game, and convert other material to for me to consider switching to a new system from the one I am comfortable with, enjoy, and have tons of stuff for.
I am getting the 4e DMG as a late birthday gift so we will see if it knocks my socks off and gets me to say I want to run it. I doubt it currently though.