Several iDevices users have reported a steady yet significant inflation of device storage memory taken by "Other" content than Music, Photos, Videos, Apps, Books...
Nobody seems to have a clue of what this "other" space is used for, nor how to bring it down to zero. Documented tricks like shutting down the iPhone, or performing a Save / Restore from iTunes won't let it go, at least on some iDevices including my iPhone and iPad.
More intriguing, such space seems to be growing at each iTunes sync. On the above image you'll see a situation where "Other" now eats almost 1/3 rd of my total available space.
What about you ?