Lord of the Rings Online has recently posted a QA team diary, with Amanda "Brynhildr" Cosmos discussing the process involved in testing the recent Volume III update for the game.
Contrary to some popular beliefs, testing generally doesn't consist largely of playing the game -- it's more about finding areas of the game that might be a bit weak and straining them to the breaking point. As the diary points out, it's also about investigating the smaller areas of gameplay that might not be immediately apparent from looking at the big picture. Travel routes, pricing on small-scale consumables, and minor text quibbles aren't easy to spot unless you're looking specifically for places that can be shored up. The full diary is worth reading not just for Lord of the Rings Online players, but anyone interested in seeing what the QA teams are actually responsible for in an MMO's production.