In the absence of any proper Windows Phone backup solution, we always give extra points for developers who back-up app settings and data to SkyDrive, the cloud storage service that all Windows Phone users are guaranteed to have already.

Now it turns out this usage has been prohibited all along, with Microsoft support posting on MSDN that using SkyDrive in this way is against the terms and conditions of the service and may result in apps being removed from Marketplace or not be approved in the first place.

Mark Chamberlain from Microsoft writes:

SkyDrive is not intended to be a free backup solution for applications. Any attempts to use it as such is outside of the intended use of the service and the restrictions present in the API are intended to reinforce this. Any apps that do this are at risk of being rejected from Marketplace, or pulled from Marketplace at a later time.

This is apparently a considered opinion and not just Markâ€™s interpretation, and is based on not littering SkyDrive with numerous files which the user will not be able to interpret without an app.

Mark writes:

The goal of the policy is to avoid the scenario whereby a userâ€™s personal cloud storage doesnâ€™t end up overwhelmed with a collection of non-human readable content, that is the equivalent of computer files such as INI and XML config files.

Microsoft also states that users should be explicitly involved in every SkyDrive upload, and prohibit automatic uploading without user intervention.

While a messy SkyDrive would be pretty annoying, I think developers could pretty easily settle on a Settings or Backup folder for example to store their files in.

Much more annoying would be to suddenly lose access to all the data you entered in your app because your phone fell in the toilet, or hopefully a bit more commonly when moving from one Windows Phone to another.

Given the horrible backup situation on Windows Phone and the fact 18 million Windows Phone 7 users will be stranded with no obvious way to protect their files and data we find SkyDriveâ€™s position pretty deplorable, and we hope they change their policy to the benefit of both developers and users, rather than maintain their current position due to some neatness fetish.

See the relevant thread here.