How can I customize the list of services that pops up when I choose to "share" something in an app? 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.
The items in the list are determined by which installed apps support the ACTION_SEND intent.  Any app that supports that intent will be included in the list.  I don't think there is a way for users to modify the list other than installing/uninstalling applications.