A time lapse (me scrubbing an 11 minute movie) of my OS X Lion 10.7.3 computer exhausting free memory, me shutting down all the apps, then opening Preview and Resizing some images to big sizes. Preview kept giving me "not responding" so I switched to Photoshop and made some really big images. Notice that Inactive memory is given back, but in the smallest amount possible, so by the end I had to stop the resize operation because it was taking so long. Then I ran purge (from Xcode) and as you can see the Inactive went away, then the PS operation took no time at all to size an image up to 25,000 pixels wide. But when it was "begging" for Inactive scraps it was so slow. You might say it's Adobe's fault for asking for memory, but that's the OS's job. And at least PS could do it, Apple's Preview just stopped responding.