Yeah, we've all talked about this a lot the last few weeks. IMO, we notice it more than we did in previous editions because the expectations have changed. 4e combat has moments that are flat-out brilliant, and if you slip off that peak into a "6-7 creatures in a room standing there smacking each other with at-wills" phase, then the drop-off from "dynamic, tactical moving combat balanced on a knife's edge either way" is very noticeable.
I don't see grind very often, and if I do, I try and take steps to remedy it quickly. I think these are the major reasons for grind, as well as the solutions:
1) Players taking too long - if it takes someone more than 2 minutes to take their action, you have a problem. Solution for this is straight-forward - work with the player to have them figure out the basic time-savers - learn your powers ahead of time, write down your attack and dmg bonuses so you don't have to add them up, roll attack and damage dice together, etc.
2) Bad luck - with combat more balanced, if the players start rolling low for a sustained period, they're in trouble, and then you're either looking at a TPK/retreat situation if the monsters are dangerous, or else grind-space if the monsters are less deadly. Not a whole ton you can do here - sometimes fudging the monsters rolls behind the screen or adjusting monster hp on the fly works, sometimes you just have to live with it and hope their dice warm up.
3) Crappy party composition - if the party doesn't have a lot of damage dealers and/or good leaders, they're going to take longer to slog through stuff. Solution - either purposely change the monsters you use against these guys (lower level, less hp, more glass cannons [presumably a low-dpr party has good defenses, so get monsters that have good attacks and poor defense to match up against them]), or suggest some character changes/rebuilds if the players are open to that.
4) Crappy encounter creation - I'm convinced this is the leading cause of grindspace. If you're good at DMing 4e combat, it has the best fights of any edition of D&D. If you stack up a bunch of hobgoblins in a 30x30 room without interesting features, it blows chunks (I'm looking at you, Keep on the Shadowfell!). If you dump a dragon by itself in a cave, things suck. The solution here is to be a better DM - 4e encounter creation is just as important of a skill as making interesting NPCs, adjudicating rules, etc - practice it and get better at it. Get good combinations of monsters that synergize well; put the fights in interesting locations; make the fights mean something; be fuzzy with your math - hitpoints are there for dramatic purposes, not as a holy law handed down from Gygax. Have your monsters move and flow - eat those attacks of opportunity from the fighter to get to the cleric behind him - the fighter will have more fun, the cleric will be terrified, the result of the combat will be less predictable, and your monsters will die faster.
The two most important lessons I've learned here are A) terrain matters SO much, and B) don't play your monsters like you play characters! Monsters are there to terrify your players, make them fear death, and then die - be careless with your hp as a monster - your goal is to do damage at any cost - a monster fighting a careful, tactically perfect defensive fight intended to maximize its survival and slowly whittle down the PCs is a perfect recipe for grindspace.
So, my final parting word in this rant here: Only YOU can prevent grindspace! There's a fantastic game out there waiting for you to DM it - go out there and learn how to do it!
