I have only been searched once in 7 times at the festival but it was pretty thorough, they opened up my tent and even went through my make up bag etc so it took a while.
I think I was just unlucky and picked at random, seemed like I was being used as training exercise as it was 3 security doing it and one was directing the other two. I didn't mind the search itself but the security guard in charge was right up in my face repeatedly saying if I had anything illegal then I better tell them or I was going to be in trouble if they found something which just felt totally OTT. They didn't find anything so I was left to go on my way, it took a while though so I got totally separated from my friends, lucky we always camp in the same spot so I was able to find them again.