Here is the first application:
This one adds an Authenticator, so your Dropbox-account is in Accounts&Sync for all apps to use (apps require their own API-key).
The account-type is "dropbox", the credential-type "key_and_secret", dropbox "secret" is returned as the password (AccountManager.KEY_AUTHTOKEN) and the dropbox "key" as AccountManager.KEY_USERDATA in the bundle.
Send To Dropbox.apk
A small app that adds "Send to Dropbox" as an additional handler for all Mime-types.
The apps will be in the Android Market soon but I want to give the People at Dropbox an opportunity to review them first.
Here is the Wiki-page where I am keeping my development-notes.
Update: I need to rewrite some of the Authenticator due to an unpublished limitation of the Dropbox-API. Stay tuned.