|Sharing in Safari on an iPhone|
However, the receiving part is still limited. iOS has built-in support for email, Twitter and more, but you can’t plug into the system with your own app. That is likely to change soon, as explained in a tweet by @chpwn:
New, private iOS 6 feature Apple is using: remote view controllers. For example: the Mail compose view is now run in a separate process.Consult  for details. I can’t wait for Dropbox to be a sharing plugin, then you can send files to it from everywhere and from it to any other sharing plugin. After the wish of better sharing has been fulfilled, I would love to be able to configure my default browser and my default maps app on iOS.