Back it up? If I back up the iPad or iPhone they only back up the stuff Apple think I should back up - which tends to be the Apps, which I could download again quite easily. The important stuff, such as my spreadsheets and word documents on there are NOT backed up - unless there's a setting somewhere that I've missed. iTunes is set to back up everything that can be backed up (but it doesn't).
I solved that problem. I never use the iPad/iPhone copy as master. If stuff disappears (as happened with all my documents when I updated the iPad to iOS6) I can reinstall from the PC. I learned that lesson the hard way. I've left the iPhone on iOS 5.something - that'll do for me.
Losing stuff - yes. Two examples:
I downloaded the Ordnance Survey maps for the area around where I live. I don't know where the OS app put them (that stuff is not described, nor am I given an option). Next time I wanted to use the OS maps: all gone.
I downloaded a Greek and a Hebrew Bible - something I use from time to time. Next time I wanted them: both gone.
That may be the fault of the Ordnance Survey and of the Bible Society for writing the apps wrong, I don't know. What I do know is that the equivalent software on my PC allows me to choose where stuff goes - and it stays there.