I've got my tongue pierced and have had for almost 11yrs now.
Mine is pierced quite far back and I don't know if that makes a difference or not but it helps it not be noticed by everyone straight away. I love my tongue ring but I got it for me, not to show it off so I like that people have asked me after months of knowing me if I've always had it.

Anyway, that was kinda off topic. I think because mine's a little further back, it's not so useful in the oral sex department but if I'm licking it can definitely be felt.
I've had FB's say it was mad, my ex fiance said he couldn't really feel it but my current SO loves it. I'm sure though that that has much more to do with the fact that I love giving him head though whereas I didn't with my ex.
I don't think I've ever heard of it being a bad addition as far as oral goes.