Since changing from Snow Leopard to Mountain Lion on my early 2009 Mini free space on the out board back-up HDD has been disappearing rapidly. After nearly 3 years of using Time Machine I still had over 240 GB of free space on the dedicated 320 GB back up HDD. In less than three months, since installing OX S 10.8 (and the 10.8.2 update) the free space has gone down to 48 GB. My usage has changed very little. The main apps I use are Pages, Numbers, Safari and iTunes. I got a camera and started using iPhoto back in May, but not so much that it made a big difference to the system. The 120 GB on board HDD still stands at 86 GB free. Has anybody else found the same? What can be done about it?