Among the surveyed games are MMORPGs that include World of Warcraft, Lord of the Rings Online, Realm of the Mad God and EVE Online. The study includes data collected on over 800 RMT items, and while the conclusions are somewhat lacking in terms of objective analysis ("nobody likes Battlefield," etc.), there is nonetheless a fair bit of interesting info on display.
Ultimately the piece reaches the familiar conclusion that RMT is here to stay and that it's OK as long as the implementation avoids the dreaded pay-to-win stigma. That said, "even just cosmetic items will breed a bitter culture of haves and have-nots if you can't reasonably get them for free in a game for which you're already paying," the article states.
Be sure to check out Massively's own RMT studies for more insight into the value offered by your favorite microtransaction games.