I see comments regarding the issue of the size of "Other" capacity increasingly dramatically going back years now. I never personally had this problem until I recorded video with my 4S. Then as soon as I used iPhoto to bring the video onto my computer and delete the original files I saw the Other capacity level jump to previously unseen levels. Ok. So I search for solutions, find several theories, none work, end up nuking the phone with a restore - and reluctantly having to upgrade to iOS5.1 in the process. Result: clean phone. That was two days ago. Today I record 12 minutes of video, bring it into the computer via iPhoto - choosing to delete the original files - and hey presto I now have 2.2GB of "Other" which makes Other look very much like its acting as a trash you cannot empty.
However, iosnoob has the right answer for my money. Turning off the iPhone did the trick and "Other" has now gone back down to 0.50 GB. So thanks! That's how you throw out the trash, apparently.