It looks like the 2011 thread surprisingly hasn't been created yet. Supre posted the initial lineup in the 2010 thread:
I am sure the lineup will be just as great though for the regular Bestival!
I went to the 2008 version headlined by Underworld and My Bloody Valentine. It poured rain practically the whole time we were there! Despite the rivers of mud, we had a blast! We are planning to go again this year! Who else is going?
And as previously pointed out, the website is awesome!