I've seen some posters saying that the tickets won't sell out for some time. However, I live in Ireland and this line up is so good that there was actually a piece about it on the news which is really unusual. So I reckon they'll sell out in no time. Better be quick!
The last 2 years i've gone the weekend passes sold out in less than 2 weeks (if I remember correctly). And I think 2004 (when Radiohead, The Pixies, The Cure, and Flaming Lips headlined), I got my pass that morning, and by the following Saturday they were totally gone.