My ds got one last xmas when he was 7, he loved it. We had hours of fun with it, they are clever little things but the instructions that come with it aren't that great, there's so much more you can do with it but have to search online for tips/tricks.
As with all toys, he did get bored with it after a while, however he does go back to it every now and again and still has periods of playing with it non stop.
Thing is, Furby's develop and change all the time. The more you play with them the more they do. So even after all this time, our Furby is still coming out with new stuff.