At least a few, online and in person, possibly more than I'm aware of. One person mentioned that he'd become an atheist as a result of observing my online debates over the course of a few months, but he never went out of his way to tell me, I only learned from following a later discussion; there might be others I've similarly influenced who've never told me.

Unlike Luke, all the people I know I've caused to convert professed to have been swayed by my actual arguments (and a fairly common reason for conversion I've heard is "I followed online debates and the atheists always had the better arguments,") but I've never known it to happen as an "aha!" moment upon being exposed to a single knockdown argument. In my experience it's always taken prolonged exposure to atheistic arguments for a sense of familiarity to build up, after which the person can have an "aha!" moment and realize they have somewhere to go from there.

Different people tolerate different demeanor, but I've never known of anyone converting someone else without making themselves likable to their targets.

In all the cases I can think of, conversion has taken a minimum of a few months of exposure to atheist ideas.