For sure, during our RL game, we really have to keep an eye on the various buffs from our cleric, bonuses to hit, marks, quarries, ongoing damage, status effets, etc...
I find it's a lot on the DM during the game to keep track of.
I think DMing 4e is going to be difficult, even live.
Consider the concept of minions. They die when they take any damage. Now look at how they fight. Look up kobolds in the MM. Minion kobolds swarm targets so they each get combat advantage (new term for flanking) over the target. Note how the non-minion kobolds get +2 for each minion in a "flanking-type" position next to the target. So the DM is supposed to track each minion and non-minion to maximize the "flanking" for the other kobolds. I assume that this applies to other monsters with minions--that's a lot of work and things to keep track of.