[JohnLBevan]

There's no need to close off an old account when you move to a new service, so you can leave your gmail as an archive - that makes for an easy spring clean too. My guess is that as cloud platforms evolve though, more and more will offer ways out - since people/companies will begin demand it before signing up as competition mounts. Those "ways out" will initially be bulk downloads (like Facebook's "download your info" feature), but over time will become more useful, offering filters on what's downloaded, pagination on downloading data, and migration APIs such that new services can pull data from the old ones without you needing to middle man the data. This isn't of benefit to providers though, which is why it relies on competition / user adoption based on ways out, and also why it will take time to become the norm.