While most social game developers are too young to post significant digital goods revenues yet, the model is looking increasingly promising for some game developers. Recent data from MMOs Maplestory and IMVU show that, at least for some, early growth can be quite strong.

In Maplestory‘s case, two people close to the company have told Inside Social Games that the company was making $1 million per month within 3 months of launch, and $2 million per month within 6 months of launch. The WSJ reported last month that the company did $30 million in 2007, up from $8.5 million in 2006.

In IMVU‘s case (the company is 4 years old but has never disclosed any metrics until this month), the company is currently doing $1 million per month in revenue, with 90% from digital goods and 10% through ads, according to GigaOm. Over 1.7 million items have been created by the approximately 100,000 content creators.

Most of IMVU’s massive catalog of avatar clothing, accessories and other objects available on its online catalog are made by the users themselves. They purchase those items from each other with IMVU credits. (A block of 1000 costs you $1.) IMVU then takes a cut of the profits for each virtual item sale, with the rest going to the individual user.

After doing the math, Jeremy Liew estimates that Maplestory has an ARPU of about $20/month, “which sounds about right and is consistent with number we’ve seen from games in Asia,” and that IMVU has an ARPU of about $14/month.

Social game developers would love to see those kinds of numbers. We’ll be tracking all the numbers as game developers on Facebook, MySpace, and other social networks grow their digital goods economies.