LinkedIn recently announced its application platform that lets developers add widgets to user profiles. Though the platform is based on OpenSocial, it's not all that open:
By making the platform exclusive, LinkedIn is discouraging new applications created specifically for the platform. To apply for consideration, you need to describe your idea and hope the people behind the scenes think it's good. While the form has the option to describe a new idea, the current crop of examples suggest you'll do better if you leverage an application you have already built.
Only a handful of applications are available right now, including two presentation-sharing applications (one from Google, the other SlideShare). Blogging providers Wordpress and SixApart each have applications to share blog posts. Amazon built Reading List, a way to share books that you have read or plan to read. Reading List is enabled by default, but other apps require users to specifically add them, choosing whether it's included on their homepage, profile page, or both.
LinkedIn is obviously learning a lesson from Facebook, as it attempts to keep the quality of its business-oriented service high. Whether a completely closed developer platform is the answer, I'm not sure. Providing developers a sandbox for their applications, with the ability to apply for being called up to the big directory might be a better approach.
A closed acceptance process is a touchy subject with developers. Apple's App Store for the iPhone has been critisized for rejecting applications for questionable reasons. At least with LinkedIn you don't have to spend hours working on your idea first.
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