I'm going to nominate the skill-set involved in participating productively in online discussion forums. :-) This involves:

• using proper etiquette
• avoiding or tamping down flame wars
• keeping track of people's identities so you can avoid crackpots and pay extra attention to those who consistently have high signal/noise ratios
• effective communication (writing clearly and concisely, reading comprehension, resolving confusions and misunderstandings)
• having a proper amount of confidence in one's ideas so as to not generate needless disagreements and unproductive arguments

I could also mention the skill-set for building a successful online community, but obviously far fewer people need that. (This seems like a good opportunity to say that I really admire the job that Eliezer has done building this one.)