One of the problems that some people have with healing surges in 4e is that you are fully healed after an extended rest, which seems "unrealistic" for some. Although hit points (and healing surges) are abstract, and do not generally represent actual physical trauma, there is a need for some, to approximate the feeling of having been bruised and battered, of needing days or weeks to fully get back to "fighting shape".
The problem with most recuperation and wound mechanics, like Mike Mearls' System Shock, the Jester's Serious Injury System, or Valorous' Lasting Injuries, is that it creates a devastating cascade effect. If your injuries do not heal after an extended rest, then you are less capable of handling the encounters you still have to face before the adventure ends. This means you end up faring worse and worse as the adventure continues. Even if the only effect is a loss of healing surges/day, it forces the adventurers to rest more and more often, or continue at lower and lower efficacy. The problem is compounded by the fact that adventures usually require the heroes to face monsters of increasing difficulty, with the most challenging encounter being the last, climactic battle. When recuperation institutes a cascade effect, the players are at their worst when they need to be at their best.
One way some DMs try to accommodate this is to downgrade the final battle so the injured PCs have a better chance. But this often feels anticlimactic to the PCs, who fought their toughest foes up front.
4e accommodates this simply by eliminating the cascade effect. You are at your best all the time. There are no wound penalties and no recuperation time. While I prefer this, some people still crave some sort of recognition that battle carries a lingering toll. I propose two solutions, one narrative and one mechanical.
The Narrative Solution
As you narrates battles, keep track of what specifically happens. When did players get bloodied, when did they incur critical hits, when did they fall unconscious and take ongoing damage? After the adventure, you should -- in collaboration with the players -- convert these events into lasting wounds. Perhaps that critical hit left a nasty scar. Perhaps the aftermath of the ongoing damage is that the player needs some extended bed-rest.
The Mechanical Solution
Each time characters fall unconscious or fail death saves, they gain 1 Convalescence Point (CP). (For an even more lethal game, grant a CP whenever a character falls unconscious, fails a death save, becomes bloodied, or receives a critical hit!) CPs represent the accumulation of damage and injuries that characters can force themselves to ignore during the short-term adventure, but that cannot be put off forever. After an adventure, characters who spend 1 day doing nothing but resting lose one Convalescence Point they've earned (until they have zero). Characters with more CPs than healing surges are unconscious (and could starve to death if not tended). Characters whose CPs exceed half their surges are slowed and dazed. Characters whose CPs are less then or equal to half of their surges are simply dazed.
Characters trained in Heal can spend an hour tending another character, causing that character to move up one condition for eight hours (i.e., unconscious becomes slow/dazed, slow/dazed becomes dazed, dazed becomes healthy.) That day, however, is not counted for losing CPs -- it just allows characters to get to where they can recuperate peacefully. The DC of the check is 20 + the target's current CPs.
Characters trained in Endurance can also move themselves up the condition chain with a successful check with a DC of 20 + the character's current CPs. This also lasts only 8 hours, and that day does not count for losing CPs.
You might also introduce Rituals and Martial Practices to remove Convalescence Points. Make it expensive enough so that characters would only do it in an emergency. Possibly, characters with more superhuman Constitution (19+) will lose 2 CPs per day of rest. Other feats and Skill Powers may make sense here as well.
Finally, you might keep a running tally of CPs. Every 10th CP a character gets, the character incurs a scar. (If you want particularly battle-worn characters, make it every fifth, or even every third CP.) This makes a CP a badge of honor!
How Not to DM Recuperation
Recuperation should not occur during the adventure. Heroes should be able to ignore their injuries through adrenalin, grit and nerves of steel. But not forever. Once the danger has passed, the players must lick their wounds and rest before the next adventure begins.
Similarly, recuperation should only apply in between adventures. It's utility as a mechanic is simply to give PCs some idea of how to narrate their perilous trek back to town or their campsite from the dungeon, and how long they spend recuperating. It allows people to engage in those lovely vignettes where they drag themselves onto their horse, which carries them to some isolated farmhouse, where the warrior drops at the threshold whispering "Help me." Therefore, DMs should not generally schedule surprise encounters while half the party is unconscious or dazed. That's simply mean, and will encourage players to become too cautious, retreating from dungeons because they have accumulated too many CPs, even though they are helthy enough to continue otherwise. And timidity simply doesn't feel very heroic. Remember, this is primarily a narrative tool, not a kludge to use against players and their characters.
Note also that characters who are often bloodied are more likely to require more recuperation time. This makes some sense, but it can cause those players to feel left out of other things that occur between battles, such as shopping or interacting with benevolent NPCs. The player whose warrior has to miss the ceremony where the party receives the key to the city because the character is in the hospice being tended to by clerics may feel that this mechanic is unfair. Always check with your players before including a new mechanic in the game.