Blizzard has been selling us in-game items for a while now; however, it has kept this to noncombat pets and mounts -- things that, outside of counting for totals for achievements, have little to no real effect on gameplay. Some of the items Blizzard does for self-profit, and sometimes it sells in-game pets for charity. People who buy the items get different reactions from the community; the sparkle pony especially got a lot of hate.
Personally, I have not bought any of the real-money pets, partially because I am not a collector and partially because I felt that paying for downloadable content should add something major to the game experience. However, I am considering buying the Ragnaros pet for one main reason: because Rags is my major epic memory of vanilla WoW, I always felt he was an awesome model and so imposing, and many of us went around saying "too soon" on Vent.
Have you bought any of the vanity pets? Do you buy them all as a completionist/collector? Do you pick and choose the ones you think look cool? Do you only buy the charity pets? Or do you avoid real money transactions in games altogether?