Hey this is my experience for what it is worth.

I went swinging with my last girlfriend. We were messing around one evening at a swingers club and I started to go down on a lady. I was stimulating her g-spot (using a 'come here' finger movement inside her,) whilst licking her clit. Soon enough she ejaculated into my mouth.

Needless to say it took me quite unawares! The sex continued and soon she was ejaculating again. She said to me during it all that she liked it when I do 'that' (pressed hard against her vaginal wall, i.e. the 'come here motion')

My experience tells me this...
1) She was used to ejaculation and had ejaculated before
2) Probably not all women can ejaculate in this manner
3) It probably isn't piss, as it didn't taste like it, and she did it several times (at least 5) over the course of the evening.
4) It was fucking cool, but a bit weird, and shouldn't be a sexual goal for any guy.

In summary she had done it before and clearly enjoyed it. But not all women would enjoy it, and it is, after all said and done, a bit weird.

Benji