The "other" space is mostly application data.
I have a lot of games on my 32GB iPad 2 and sometimes I have up to 8GB of "other" data. The application data in my case is the game saves. I also have an app that hides files and images behind a password protected GUI when the app opens. All the files that I have in that app would show up as "other" in iTunes because iTunes only recognizes music, videos, photos, books, and apps. Anything else goes under "other".
From my research, sometimes you can reduce the "other" portion by syncing your iPad with iTunes, then under the summary tab, click the check box for "open iTunes when this iPad is connected". Then sync your iPad again, and finally re-check that same box and sync the iPad for a third time.
Let me know what your experiences are after you try this or if you have any more questions.
Sorry if I rambled and that I don't have links to articles to better show you.
Use iFile or iFunBox and go to var/mobile/media/iTunes_Control and see if there's any extra crap there. At some point I had like 2 gigs of extra files (podcasts and videos etc) that I 'deleted' a while ago, but didn't actually get removed for some reason.
When I removed them, my 'Other' category shrunk to less than a gig.
When I plug my iPad into iTunes, it shows that I have 2.4 GB of "other" data on my iPad. I can't imagine what this could possibly be. That's quite a bit of space...any ideas?
It's also cache items, such as Spotify or Amazon Cloud Player that download recently played songs.
It is basically data that iTunes can not explicitly get to, it's outside of iTunes control.
I have had to do a restore a couple times because I download too many tracks from Amazon Cloud Player. Once I realized the app provides no way to delete the downloaded songs and iTunes can't do anything about it, I stopped using that "feature".