The Thief is described in as "a master of stealth and surprise," able to set traps, "travel through the shadows, vanish into thin air, or steal items from their opponents and use them as weapons." Of course, as per the rules of RPGs, such a skillset means they're lightly armoured.
Thieves will use a combination of ranged and melee--swords, daggers, pistols and shortbows--and can equip different weapons in each hand. Unlike other classes, the Thief's weapon skills have no recharge times, instead relying upon a resource named "Initiative."
While very little was revealed about the Thief today, the class will be playable at PAX East, which begins on March 11. If you're not going to PAX but are in the area, you can also try it at NCSoft's 'Boston Meet and Greet' at the Westin Boston Waterfront Hotel on the evening of the 11th.
Guild Wars 2 is due "when it's done." Whenever that turns out to be, the subscription-free MMORPG will be released on PC.