The most important job the GM has in a combat in a crunch-heavy RPG is to keep it moving. Number one on the list of pace killers is the pause that results when the table loses track of whose turn it is. With the aid of an initiative management program for my Palm, I’ve gotten way better at keeping the NPCs going.
In 4E I’m running into a fresh problem, stemming from the new turn structure. Now you get to do up to three things per turn (or more if you spend an action point.) You may also make saves, take free actions, and so on. Consequently it is no longer immediately apparent that a player’s action is over. Just because he’s impaled that goblin for 30 points of damage doesn’t mean he’s done. Players are not yet accustomed, however, to declaring that they've completed their turns.
Every second that passes when no one is acting is deadly to combat pacing.
I’ve tried to get the players to call out “pass” when they’re done, but it’s a hard habit to get into. The answer probably lies in a prop — or, as it did with GUMSHOE scene enders, a sound cue. I’m considering a bell for players to ring when they’re through. The trick will be to find something that isn’t too silly or distracting. A dinner bell is a little too rarefied, I’m figuring. Maybe one of those chrome dome ring-for-service bells would allow players to conclude their turns with an appropriately aggressive flourish.