For me several years ago now, when it was less commercial, but i was put off from festivals in general when i got so ill i nearly died after camping at a festival at the Forest of Dean (beautiful part of the uk) on what turned out to be a poisoned field!
You can watch this years festival live on the BBC iplayer, (safer and less muddy!)
I am not sure if non uk peeps can see it, I sure hope so!