Randarak: In my own personal experience, and one could probably say this about almost anything, it varies for each individual. I can honestly say that there isn't a single woman that I have had sex with whose face hasn't received a facial from me. So its not like its a rare thing to find a woman who likes it. It really is simply a personal preference. Although, sometimes it can happens whether you and she have prepared for it or not!
In the end, one simply needs to ask if she likes it or not, but not as you are about to do it to her. If you do that, you'll probably never get to do it again.
And a tip for the ladies who've NEVER done it: Close yours eyes, I'm told it BURNS!