The first two solutions are iOS6+ only, and the UDID never worked on iOS6. People who can live with cutting off iOS5 don't have a problem by definition.
Ubiquity container: Does anyone use and track this? How many % of people have iCloud enabled for third-party apps? (Just asking because I turn this off on all devices; I don't have any app that uses this, so all I am disabling is abuse)
Some apps push data into the cloud without asking/having an option. For me this was Screens VNC, which synced semi-confidential information across my two computers without asking (all my bookmarks, except for the SSH/VNC passwords).
Arguably the external IP, SSH port, SSH username, internal IP and internal username of my client's confidential computer are only "security by obscurity", but I'd still rather have everything on my hard drive only by default.
Ubiquity container: Does anyone use and track this? How many % of people have iCloud enabled for third-party apps? (Just asking because I turn this off on all devices; I don't have any app that uses this, so all I am disabling is abuse)