Now it appears that such exuberance has infused the expanding Facebook universe, even though no one has yet proved it is possible to build a profitable business with sustainable revenues on the site. Some developers report earning tens of thousands of dollars in advertising with the applications they have created. Yet their applications are mostly running ads promoting other Facebook application

Yet there are questions about the ability of these Facebook-inspired businesses to create sustainable revenues. Developers are restricted to placing advertising on their ?canvas page? - the portion of the site through which users install and interact with an application. Facebook does not allow developers to advertise on users? profile pages, where the applications themselves are imbedded.

Several companies have created networks to funnel advertisements to canvas pages, and Facebook itself has indicated it will soon introduce its own ad system for developers. So far, most of the ads on canvas pages promote other applications whose creators are seeking exposure.

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