As part of Twitter’s ongoing strategy to craft a more unified user experience directly inside Twitter.com and their mobile apps, Twitter has now removed Find My Friends API access for Instagram users.
This means Instagram users can no longer quickly use the Twitter API to see which of their Twitter contacts also has a Instagram account.
Of course the Find My Friends feature is still available for Facebook, where you can quickly look up your Facebook friends list to see who is also on Instagram.
Twitter recently also closed off their sharing agreement with LinkedIn and it seems they may be isolating developers on their platform, something Twitter needs to treat very carefully with.
Of course you can still share your Instagram photos to Twitter via their posting API, as you can with Facebook, Flickr, Tumblr, and Foursquare.