i had one for a few years until i took it out this year. a lot of guys notice the difference (positive) with blowjobs but kissing-wise it's not that much different. it can be annoying if it hits the guys or your own teeth but that hardly happens with a good kisser
I have one and am always pleasantly surprised when I make out with another guy with one. It doesn't happen very often, but when it does it's fun. With getting head from a guy with one, I've always been able to tell the difference. I like it better if the person is pierced.