Hey everyone!
I’ve just discovered this today.
I’ve been happily modeling and rendering, and as I’m doing static images, I selected the option to cache BVH for faster re-render. I checked as well Persistent Images option (keep render data around for faster re-renders) - probably this was the one to cause me trouble.
Anyways, happy happy with my blending, up to a point where my HDD had only 2gb left. And an hour ago I only had 25mb left! I thought I’ve installed too much software, which was pretty sure I didn’t.
And then it came to me - could the BVH cache be stuck around?! Then I found a similar question at blender.stackexchange (http://blender.stackexchange.com/questions/9291/how-can-i-change-the-directory-used-to-cache-bvh)
So I went to the cache folder ( c:\Users\username\AppData\Roaming\Blender Foundation\2.71\cache ) and all the other Blender versions caches as well to find the missing HDD space! In the 2.71 only there was 78gb! And all versions combined I had more than 90GB of used space!
My gess is I shouldn’t turn on the Persistent Image option without taking this into consideration. But if there’s someone else that knows more about this question, please reply.
Turns out this issue has already been reported, and it appears more of a design consequence than properly a bug.
Anyway, don’t know if anyone went through this same problem or is it just me and my dumb mind, so I leave my experience here, there can be more like me out there 
