This is an interesting eWeek article discussing how Microsoft Dynamics Live CRM will include an on-demand marketplace for partners to showcase their company, applications, solutions, and customers.  The article says that this is similar to Saleforce.com's AppExchange. 

The concept of an on-demand environment for customers to shop for solutions is fantastic.  In my experience many customers do not want just simple vanilla CRM.  They have specific customization needs - either vertical requirements (ex. real estate, 311 case management, etc.) and horizontal requirements (marketing analytics, event management, etc.).  This marketplace will enable a customer to shop and buy functionality a la carte. 

If it catches on it may spawn a new developer industry.  For a good example see this article in Redmond Developer also published today.  The first Facebook developer conference was held recently with over 750 developers in attendance!  Facebook is taking off in large part because of the many creative applications that it's partners have developed for it's site.