4th Edition intoduces the concept of "milestones". A milestone is reached any time the party completes two consecutive encounters without taking an extended rest.
Reaching a milestone has two effects. First, it grants players an extra action point, which can be traded at the end of a player's turn to immediately take another standard, move or minor action (that's "or", not "and"). That's good, but not wonderful, as you can only spend one action point per encounter in any case.
Secondly, it grants players another use of a daily equipment power. Normally players can only use one daily power granted by equipment per day, no matter how many such powers they may have access to. (If you have a daily on your armour and a daily on your boots, for example, you can use one but not both.) The milestone allows a further such use.
Milestone benefits vanish after an extended rest; no matter how many you've accrued, sleeping sets you back to a single action point and a single daily equipment power.
The commonly cited intent behind these powers is to "reward players for a long adventuring day". That's something of a misunderstanding, though. Milestones don't reward long adventuring days, they merely make them less punishing. Given an unlimited pool of time, it is always better to take an extended rest after every encounter, to refresh your daily class powers and regain your full pool of healing surges. If the benefits of a milestone outweigh the cost of surviving two encounters without resting, then your encounters are probably too easy.
Milestones are a very poor way of balancing extended rests. They don't encourage players to press on, they merely make them less angry when they're denied a rest for long strings of encounters in a row. DMs who don't want their players taking a nap after every fight are going to have to introduce time pressure into every story (which generally improves the story, so not much of a loss) or repeatedly make it too dangerous to camp (possibly realistic but rarely fun).
Wizards of the Coast should have gone down a different path. Instead of hitching daily effects to the concept of resting, they should have connected them to some narrative element. "Daily" effects should instead have been "once per session", or, if you don't trust your GMs to wrap up game sessions at an appropriate moment, "once per chapter", with the GM having the explicit power to declare a "new chapter" at any appropriate lull in the action.
It would have been more consistent, too. We already have the concept of an "encounter", a unit defined more by narrative than by time; it seems odd that daily effects don't follow the pattern.