Apple has an open developer's platform for the iPhone, of course. Facebook has a developer's platform for writing apps, as well. Ditto for Twitter, Google Android, Blackberry, and Salesforce.com. LinkedIn finally gets it. Mind you, fifty million users are nothing to sneeze at (unless you are Facebok with 300 million users - Meow!).
Tweetdeck has already promised that it will be adding a LinkedIn app in its next release. Microsoft says it will use LinkedIn within its new Outlook 2010 social connector release coming out in a few months.
LinkedIn, I have been worried about you. I personally haven't looked at my profile on your site in months (Plaxo, for you it's been even longer). I think you need help. Hopefully this will put you back in the game.
I really want LinkedIn to succeed. I think we need a powerhouse social network that is strictly business. As much as I love Facebook, I do struggle with the overshare issue of my personal life with professional "friends".