In Deathly Hallows they traveled every day to a different place, for months, all over England. How could they know so many places? Or does apparition work even when you don't know the place you are going? And it's not that they traveled some miles near the previous place:
The weather grew colder and colder. They did not dare remain in any one area too long, so rather than staying in the south of England, where a hard ground frost was the worst of their worries, they continued to meander up and down the country, braving a mountainside, where sleet pounded the tent; a wide, flat marsh, where the tent was flooded with chill water; and a tiny island in the middle of a Scottish loch, where snow half buried the tent in the night.
Edit: I found a quote in the Half-Blood Prince, just before they went to the cave for the locket. that shows pretty clearly that you can apparate somewhere you haven't been before:
“Professor,” said Harry quietly, as the gates at the bottom of the drive came into view, “will we be Apparating?” “Yes,” said Dumbledore. “You can Apparate now, I believe?” “Yes,” said Harry, “but I haven’t got a license.” He felt it best to be honest; what if he spoiled everything by turning up a hundred miles from where he was supposed to go? “No matter,” said Dumbledore, “I can assist you again.”
Edit 2: And this contradicts the last one... So if they can apparate to a place they don't know why don't they apparate right outside Luna's house?
Where do the Lovegoods live, anyway? Do either of you know?” “Yeah, they’re not far from my place,” said Ron. “I dunno exactly where, but Mum and Dad always point toward the hills whenever they mention them. Shouldn’t be hard to find.”