Our friends at WoW Insider (disclaimer: I'm a lead blogger over there) have good news for Mac World of Warcraft players who want to support one of their favorite sites. Wowhead, which is one of the premium online databases of all the items, quests, and NPCs there are to find in the game, has released a Mac client for their info-gathering spiders. Basically, you start up their app while you play the game, and it automatically pulls info to populate the database.
To answer your question, no, you don't get anything from gathering information for them, save for the pleasure of knowing that you're helping to support and fill a popular database (that most WoW players have probably used for free before).
But if you're a Mac player who's used Wowhead in the past and wouldn't mind helping them out, here's your chance. The client is a quick free download from their site.