How do you refer to someone of unknown gender?

The question of gender-neutral pronouns has been discussed here in the past. But I’d like some advice on how to interact with a person of unknown gender. (I believe this person identifies as genderqueer.)

Since there is no generally accepted neutral pronoun, if I were to speak about this person in the presence of others, what is the acceptable way of using a pronoun? Should I avoid it and restructure my sentences to only include the person’s name? Should I ask the person how s/he wishes to be referred to? What’s your experience? If you are genderqueer or otherwise self-identify as anything other than fully male or female, what is your preference?