Many apps give you the option to "Share" whatever it is you are looking at (or watching or listening to). This usually manifests in the form of a popup list of services that include: Gmail, Facebook, Twitter...) The list seems to be the same from app to app. How can I change what services are listed on this popup screen? Is there any way to change, add, remove, append this list? I'm running Android 2.2 on a Moto Droid 1.

While I can chose Share by a contact on my Droid's contact list, the Droid on the other end seems unable to open, or really do anything with, the resulting attachment if I receive it via Gmail or the normal mail client. Am I missing something? How do I import what I've shared?