The players cleaned up the wraiths without a huge amount of trouble, but it did cost them a half-dozen surges. This left them wary of continuing to delve into the woods. Here my favorite part of the encounter comes to be. After defeating the Wights, the players decided to try and find a place to rest. They wagered that the forest should be safe after they dispatched the Wights and their commander... Oh how wrong they were.
The most overlooked part of Encounter Design.
This could almost qualify as a post topic in and of itself.
In my opinion the most overlooked part of encounter design is the repercussions and immediate follow up. Immediate follow up incorporates those things which should affect the players in between this encounter and the next, if this is a dungeon. Or the next hour or so of non-combat time. While repercussions influence the entire adventure from this point forth.
So what were the repercussions and Immediate follow up here?
Immediate follow up: Having slain the leader of the Wights, who had been holding the band cohesive, the spirits of the forest have been released, and are not to happy with the players. Any attempt to rest within the woods is now far more mentally taxing than it should be, there is a malevolence and weight to the air. The players may also run the risk of running into more corporeal Wights. These fights aren't meant as full encounters, but each run-in should have an effect, perhaps charge the players a healing surge each time they run into a wight before it is unceremoniously slaughtered... That will start to worry the players, instilling the dread of running out of surges and finally being dragged down from attrition.
The repurcussion of slaying the Wight battle group was that the Lich who now lives within the ancient manor keep knows that something dangerous exists in the forest, and defeated his lieutenant. A particularly paranoid individual, he now sets about setting his traps for the PC's when they decide to step further into his domain.
This encounter taught me that varied enemies is paramount to success in 4e encounter design. But an easy battle shouldn't end without some danger to the PC's, a little bit of dread can go a long way... Be sure that the battle ties into a larger scheme of things, and is not just there for it's own sake.