Hey,
the most frustrating in this game is how hard GW2 is on the mouse, especialy LMB. Wanna buy 100,000 drinks for the Thirst Slayer achievement? No problem, only 200,000 clicks to buy them, and 200,000 to drink them (and maybe a new mouse in between? 
). Even single RMB click would of made a huge difference.
Developers, please make some sort of quick buy system. RMB click would be nice to have, but some sort of buy (use) stack of items is a must have. Clicking is not fun in huge quantitys!