Personally I think that players attempting to sleep in full armor by default is very 'gamey'. Players will find themselves without roleplaying XP for the session at the very least if they insist on that.
In my games you can sleep in armor but you can only regain half as many healing surges as normal and can only have a maximum of 1 less than normal. Taking a nap/rest in full plate armor in between waves of a seige (for example) is fine, it will re-energise you pretty well, but not like a real rest.
I also make assumptions about a characters off-screen habits based upon the way that they act on-screen. The guy that always sleeps in armor will smell really bad and generally does not care about hygiene very much, which other people tend to notice. The guy that insists on always being armed and near an exit is assumed to be paranoid and more than a little delusional/shell-shocked. NPCs deal with them accordingly.
I agree it could be "gamey." Of course, I've played in enough groups where the DM routinely uses nighttime ambushes
because he knows the players won't have access to their armor bonus that I've become a bit paranoid about it. "Gamey" DMs breed "gamey" players.
On the other hand, if a small adventuring party was in enemy territory and a nighttime assault was a real possibility, it would make sense to sleep in armor clutching their weapons. Soldiers throughout history occasionally have had to do this during sieges and before big battles and apparently could still function and win the next day so, while it certainly isn't comfortable or as restful as a night on a Tempurpedic mattress it isn't incapacitating or seriously debilitating if done only once and a while.
So for example, the half-healing surge thing seems a bit strong. Any graduate student can tell you that you can pull an all-nighter before a huge presentation, due-date, conference, or whatever and make it through the day on pure adrenaline; you just can't do it on subsequent nights. In another, more "physical" instance I slept in Yosemite with insufficiently warm clothing (I learned a valuable lesson that night) and on uncomfortable, rocky ground (but in a tent), got at most 2-3 hour of restless sleep and then climbed Half-Dome. I obviously did not lose
half of my total life force as a result of this awful night of sleep. I was darn exhausted though and if I were forced to do it again the next night, I would probably have become seriously ill and unable to function. On the other hand, I am not a legendary hero with super-human strength either.
If I were to do this I would probably let players sleep in their armor once and while without penalty. If they did so on two or three or four nights in a row I would subject them to an increasingly stiff endurance check; they would begin to lose access to more and more surges, start gaining penalties to perception, and insight, and take additional surge "damage" if they tried to cram multiple encounters into the same day. I think you can adjust the severity of the penalties according to the power level of your campaign. I'm guessing in the epic tier when the characters are all demi-gods and can warp space-time, a couple of nights sleeping in their armor is not going to phase them much.
Of course, I am not one to tell someone how to have fun so use whatever system you'd like.
