I was going crazy with my backups continuing to fail on me time and time again, but I've solved it! When Apple pushed out the iCloud control panel upgrade for my computer I installed it and noticed that I had a 63MB backup already in the cloud[this backup was made in the beta days] and I had fresh restored my phone when I upgraded to the GM so it ended up being a virtually different device.
What I did to fix it? Delete the old backup! Once I did this my device immediately started to backup and all of a sudden a 1.2GB backup showed up in the control panel with three hours to go.
What I did to fix it? Delete the old backup! Once I did this my device immediately started to backup and all of a sudden a 1.2GB backup showed up in the control panel with three hours to go.