I went through a bit of a phase where I was quite into the idea of it, so once tried it with a girl i'd seen a couple of times.. she was really clean, great skin, clear face, etc... went into bathroom, and I got in the bath and she stood over me. Started on my body, eventually ended up pissing into my open mouth. I didn't drink it but it was really hot regardless.
The anticipation, and for some reason watching her drink glass after glass of water beforehand was a massive turn on.
Also, the fact that she clearly found the whole thing a little odd, but was happy to go along with it for the experience of it.. it added to it somehow..