Much like any other MMOs that does not require a subscription fee, Guild Wars 2 will feature a microtransaction system that will allow players to purchase Gems, which can be used to purchase cosmetic items or temporary conveniences. Many players were worried that Guild Wars 2 will turn into another Pay-to-Win MMO, so ArenaNet has come up with a detailed explanation on how microtransactions will turn out.
Guild Wars 2 will have three currencies: gold, karma, and gems. Gold is the standard tradable currency that can be earned by all players in the game. Karma on the other hand, is not tradable but is rewarded to players for completing events. Lastly, gems are the tradable currency that is bought with real money. ArenaNet has made it very clear that it will not affect the playing field for all players. Players who do not wish to spend real money can still obtain cash shop items by trading for gems with gold, and ArenaNet believes that this will allow players to create and decide the market.
I personally have nothing against microtransactions, as long as they do not give other players an unfair advantage. I think what Guild Wars 2 is trying to do is the same as Team Fortress 2. Think of gems as keys and gold as refined metal in Team Fortress 2, it's pretty much the same thing. I, for one, welcome the microtransaction system.
Image source: http://www.ikogamer.com/2012/03/21/guild-wars-2-micro-transactions-explained