I had an ex-girlfriend with a tongue piercing and it did honestly hurt, especially after she was down there for more than a few minutes. That's just me though, surely not everyone feels that way.
My current boyfriend is the first person I ever enjoyed oral with -- before it was just "yeah yeah, nice, now stick it in there and let's get this over with" but I think the difference between my former partners and my current is that my boyfriend LOVES to eat me and will do it for two, three hours at a time. He often sticks his fingers in me, which drives me nuts (in a good way)

With other people, oral sex seemed like a "duty" so I didn't get much pleasure out of it (strange, because I've always loved to give) but with this partner, it's just plain phenomenal :^)