I have an iPod Touch 4G, not jailbroken, and was surprised to see other' increase from 0.37GB to 4.5GB for no reason at all. Every time I deleted something, the 'other' would grow. Every time I synced an album, the 'other' would grow. I restored the iPod 3 times, twice setting it up as a new device - and this is what happened after I added a couple of albums and photos after setting it up as a new device:
Almost 3GB of 'other' on a 'new' device is wrong! I called Apple and they told me to uncheck the 'sync' tabs etc, but to cut a long story short, nothing worked at all until I 'erased all content and settings'. This reduced the 'other' to almost nothing, but within 3 syncs, it had grown to almost 5GB. Finally, in desperation, I tried one of the tips here, and swiped all the music off the iPod from the iPod itself (strangely enough, none of the music got deleted). I then switched it off and back on again, plugged it in, and before I hit 'sync' - this was the reading:
After I added a couple of albums and videos- THIS was the reading after the sync:
As you can see, I have NO 'other' any more (which isn't right) and total capacity is 32GB instead of 28.5GB. Now, I only see the correct capacity and the 'other' category before I sync. After the sync, I see what's in the screenshot above. It's all very strange, and no matter how many times I sync, I only see the 'true' reading before the sync - and 'other' hasn't grown at all. I just have to remember to deduct 3.5GB available space as the capacity is reading incorrectly.
Obviously, this isn't the ideal solution, and something is still wrong. But for now, I can live with the wrong reading as I can see the correct one before the sync in the second screenshot.