This is seriously not cool. This happened to me too in OS 5.1.1 and I just spent the whole ----ing day troubleshooting what could be taking up 2.5 GB (same size for me too) of "other" data. I've deleted apps, emptied trash folders in mail, deleted caches, even wiped all my music because for some reason whenever I sync, iTunes thinks I have an extra GB or two of music, pushing me over capacity.
So I tried to restore to get rid of the extra weight, but I'm not even allowed to restore the OS version I'm ALREADY RUNNING. Now I see that this update I never wanted or allowed is holding my phone hostage. To borrow the car analogy, it's like you buy a car, it's working fine, then one day all but the driver's seat is full of sandbags you can't remove. They're bogging down the car and limiting what you can do, but your only choice is to take it in to the dealership and make a one-way trade for whatever the dealer feels like giving you instead. HOW ABOUT JUST LETTING ME USE WHAT I ----ING BOUGHT?
This is untenable. Even though I have a really large investment in iOS over the years, I think it's time to walk away. If Apple can't even respect their users' wishes and instead insist on hijacking their devices despite their preferences, then Apple products are no longer a viable choice. We're paying top dollar for devices we can't even PRETEND to own. I'm not crazy about the competition, but if there isn't a good solution for this, they give me no alternative but to walk.