Last December I started playing League of Legends. It has been 8 months since I started. In that time they have released 8 new champions at about $10 each (I have not bought all 8 champions), they have announced a player base of 15 million accounts (that includes abandoned, multi or smurf account, etc), they have declared the creation of a new game type (Unreal Tournament is calling, you know, from the 90s), and they have updated the client to let you know how much money you have spent with them.
Now, as I play, I've found that after playing games with RMT as a revenue source, it becomes easier to spend money again on it, and on other games as well. My journey started with Gaia Online, where I spent a small amount to buy an outfit for my anime style avatar. It was just because I could, and I wanted to look nice. But that small $5 transaction somehow allowed me to understand RMT and microtransactions.
In League of Legends, I have spent $140. With those $140 I have bought: 17 champions (most were on sale), 18 skins (again most on sale), and 3 bundles (that is 3 champions and 5 skins). At the same time out of the 64 champions I have purchased, only 1/3 have been with real money. The rest I bought with IP (influence points) which is earned by playing the game.
At no point do I feel swindled by Riot for this. Considering the idea that I'm spending $20 a month for 7 months (I didn't buy RP for August), and that I don't have to ever spend money again for the game, and that I never had to spend this money, I'm not unsatisfied. I paid $15 a month to Blizzard for 4 years and that was with purchasing expansions, and now I can't even play my Shaman. There is a lot to be said for F2P, and Riot is showing how F2P done right can make a customer feel proud of having spent money on the game.
There is a lot of ways a game can make money on the F2P model, but the best bet is to make a good game, sell non-power items, and respect your customers. To be fair, the first and the last are really hard.