Having the same issue on my ipad 3 (Sorry the NEW 2) and I am only backing up my bookmarks!! (I am not backing up anything else, once again I am getting 5GB as the reported free space
Apple got me to reset my network settings which did not help, and now want me to restore the entire device.
Ironic since I can backup fine with dropbox, skydrive, google drive, sugarsync both with client apps and with Readdledocs.
Problem is, I want a basic IPAD SYSTEM backup, with the third party providers do not seem to have (like a bare metal recovery program for a computer) nor would I trust since they are not from the same vendor.
So I will prepare to write off a day and visit an apple store in the future....
Think the real issue is not the apple so much as the communications with icloud back end. FYI I was able to log into the icloud at www.icloud.com and noticed that some (calandar) info was there (once I turned calandar on as a test for additional backup) so even with the error SOMEthing has backed up at SOME time.
This is the web front end for the cloud storage. It must be either the IPAD is reporting to the ICLOUD server an incorrect amount of data, OR ICLOUD is simply not functioning correctly, which makes you wonder about using the service if you really needed it.....(it may not be there).
I think apple need a better Service Level Agreement with Icloud, particularly if a paid customer.Since my job is not a beta tester or a quality consultant for apple I will leave it to them to resolve their issue, and until then my money ($19 per month) will go to dropbox!
Maybe it is backing up SOME data at its discretion, its a bit like the HDMI (geniune) connector that says when first plugged in that "this accessory is not supported" (thats even with 5.1.1 IOS) but functions anyway....