My own opinion might be summarized in this way:
There is no need for a RULE to adjudicate long-term damage, but there is a need for an EXCEPTION to adjudicate long-term damage.
It is this philosophy that has guided my campaign since about 1983, in any game with truly abstract hit point systems.
Many here are right - in cases where the story has ended, or a long pause is possible, the addition of "long-term damage" makes no sense...I put that in quotes because the damage is "long-term" only with respect to the in-game calendar ('We camp until June'), and has no lasting impact on rolls or activities, and therefore is only a fast-forward step in the adventure. Because of this, any RULE (meaning in my post something that MUST be observed) for long-term damage would lead to a lot of these FF moments.
However, I have often run stories where there is a time pressure - - the villains will open the gates to Hell in three days, the Marquis will marry the maiden at the next full moon, etc.
In those cases, it is no great difficulty to assess long-term (okay, maybe MEDIUM-term) damage impacts. When it would make sense, I typically introduce the possibility of lasting damage under two situations (which may not work in 4E) - - 1) Critical hits doing damage within a point or two of the maximum, delivered by foes who are above the level of rabble (i.e. - a very lucky kobold won't put you out for a month), or 2) dropping to 0 hit points. I am also FAR more likely to do this in the second situation, because #1 can happen through no fault of the player, but #2 is more likely to result when the PC just isn't smart enough to avoid trouble.
The issues are never completely debilitating, but are often large enough to make a dent in their power (penalties of 2 or more to a stat, move penalties, skill/attack penalties, etc.). It can't be too large or you've taken a player out of the game (and since we only play once a month, that's a rotten thing to do even if the player was being stupid). I have also been known to give someone NO penalty, but a 'bleeder' -- a wound that could reopen (normally any time THEY roll a 1 during the duration of the effect, or an opponent rolls a threat) doing a point per round until closed with C*W.
Sorry for the essay...should have just said that I like these things when they are part of the storyline, but not as something that always occurs when XX happens.
Also...my old brain remembers one of the books (1st Ed DMG????) having a game description where someone takes an arrow in the leg and loses Dex...but I could be wrong.