Perception skills were already very important in 3e. Combining the four skills (Search, Spot, Listen, Sense Motive) into one and adding tracking to its game functions has just made it that much better - making Perception the most important 4e skill IMO. High Perception means not being surprised, being able to spot & attack hidden creatures, finding hidden treasure or clues, avoid traps & other concealed dangers, being able to track an adversary, knowing if this important figure is lying to you... all highly important abilities in the adventurer's line of work.