I have an interest in virtual worlds SecondLife, OpenSIM etc and I came across IMVU. Its essentially a 3D Chat environment that has the tag line "Live the lifestyle you have always dreamed of". Like most virtual worlds the avatars are attractive and let you have access to the lifestyle accessories that are often out of reach for the normal person.
I have added a short promo video below showing IMVU.
The usage model is around people meeting and communicating in a cartoon environment and usage is driven through the use of credits that can be earned from chatting and accessing the system. The aim is to get users interested enough to start purchasing credits with real $$. It is quite immersive but not in the same way as SL as it has limitations.
I have included a quick Slideshow of the environment to give you more of a feel for the UI.