No disrespect intended to wrecan, but I read his improv guide and it's seven steps. I can't see that being used in a game very often, and a game where even just using your stock power loadout is often compared to bullet time in The Matrix (i.e. way too slow to allow any of the other pillars of gameplay any air to breathe in). Thing is, I don't want to look at powers and decide what to do in this room or that situation. If I'm playing a big strong fighter, or a swashbuckling rogue, or a shape-changing druid, I can think of all manners of things to do on the spot without the need (or desire) to simply put my card down and say "this is what happens now, will ye nil ye" to the DM. It removed the DM from the equation from adjudicating often simple things that shouldn't be tough calls. If you're in a room full of barrells propped up with a perch, chased by orcs, I run by and say by the way, I kick the prop down as I run by them to cause them to roll. Why do I need an "encounter" power to do that? The DM quite often, for trivial or clever or cinematic things, would just say "ok, yeah you knock that fruit cart over, causing a raucus, it gains you and your friends a 1 round head start to get away".
Really do not like "auto-happen" cards that replace creativity and make all the fruitcarts or barrels that the DM either describes are in your surrounds, or aren't. I just can't see that "power of skill" working without props in the scene to use - PCs will probably not be carrying a load of garbage around just to make a tiny area of debris -- and what if you're in an empty room? Shouldn't work. Just...no. And you take this "Power of Skill" instead of some other, much better feat or power at that level. What I'm saying is, for the love of improv I think relying on cue cards that automatically work is a way to ignore what the DM describes in the scene and having to think on your feet to actually make it happen. I think it cheapens the job of the DM, gives players no incentive to actually listen to the DM (I've seen this in every edition, but much more so in 4e, since improv is so suboptimal a strategy / lackluster next to just killing stuff).
"Plot coupons", no offense, sounds like a terrific way of describing a gameplay mechanic that I wish had never been made a part of D&D. What power of skill does is reduce the actual room or alley or environment your PC is in to a set of squares, and everything within them, other than "difficult terrain" or monsters are fluff.
The best set of rules to improvise are those that get the heck out of the way of your creativity, and require you to FOCUS on what the DM is saying, and what he / she is describing to you. The rules I'm describing are, of course, ability checks or skill checks, or proficiencies, and should be only used appropriately, and with DM fiat. Players being able to dictate the narrative with "this happens" is just not true to the spirit of the game. At least not in any that I want to play in. DMs I've played with love when you do creative and interesting things, just could never get their heads around the 4e way of doing it. Wrecan's positive contributions to the 4e forums over at Wotc headquarters might be held in high regard by many, but the improv guide I read of his is just so impractical, and is in such a 4e-esque frame of mind (hey, this simple encounter is already taking three hours, what's another twenty minutes to adjudicate how we're going to knock over this bolder from the roof). Sigh....at a certain point we just wanted battles to be over because they long ceased to be exciting any more.
I work 60 hours a week, and just don't have time to play a game where every skirmish turns into an hour long affair. You get nothing done. One of my first posts here mentioned how when I joined some pathfinder groups it was such a breath of fresh air. To me, that was playing D&D again. Sure it's not perfect, and it is very rules heavy too, but once you have your character made you can do a zillion things per session, and you had bloody well pay attention to what the DM is telling you if you don't want your PC to wind up in an early grave.