Chris Anderson, author of The Long Tail, uses free-to-play web games as a case study on conversion rates for freemium products. I wrote about the conversion and monetization rates in this world two months ago as a followup to my GCDC presentation from last summer. I can't really think of a better example of freemium model than Habbo - a freely accessible service with high engagement and a large audience really gets to utilize and showcase the model at its very peak. The only thing missing is even easier micropayment models. We'd love to use the iTunes store for selling Habbo items, for example.