Model: 3.06 GHz late 2009 iMac running Mountain Lion with 8 GB RAM and 500 GB HD Primary Applications: Photoshop CS5, Lightroom 4.4 working with large Raw images Symptoms: Usually works okay (not great) for a couple hours, then gets really, really, really, really slow Examples include: taking 20-30 seconds to flatten a file in Photoshop, taking 10-15 seconds to render a full size image in Lightroom; watched an image being flattened in Photoshop on Activity Monitor and the CPU and RAM seemed NOT to be doing a whole lot. It seemed like it was mostly just waiting for the HD to respond. Strange Behavior: Was reviewing hard drive availability looking at my wife's (primary user) user name and it read that it was using 266 GB. Then I checked on MacintoshHD to see what the total usage was and it said 414 GB. Naturally I'm wondering what the heck is using an additional 150+ GB; so I start checking applications, library, etc and I'm only seeing maybe 35 GB or so. So I go back and check my wife's profile and all of sudden it says it's using 365 GB. I double checked with my wife to make sure we both saw the 266GB 5 min before to make sure I'm not going blind and she agrees it said 266. Has anyone ever seen this? Is this an HD going bad? Side note (probably unrelated but just in case) her monitor seems to be yellowing from the bottom up.