I have seen these in many successful forums, and I find it very interesting and fun. However, it does require some work to manage, and make sure every transaction is handled properly.
The basic concept, for those who don't know, is for a section used to spend "cash". This cash is an additional meter, shown in the left of each of your posts, under Reputation. We can call it "VS Cash". This "VS Cash" can be earned by posting, some sections earn more "VS Cash" than others. The shop section is where users can request to transact their "VS Cash" for items like professional signatures, avatars, be creative.
I can volunteer to help run the Shop as a Shop Manager of some sort. This new position would just be to edit prices, make sure transactions go through with the Admins, who have to deduct "VS Cash".
I find this feature very fun, and could make our forums even better.