Less than one year with Mac now. I've been using David Pogues "missing manual" to help learn within Tiger. Read about disk utility and repairing permissions, but never used it until last night. I got my iMac in June 2007. Everything seemed to be running great until I bought and installed all the recent MacHeist applications. I also added an external in Dec, so maybe that might have screwed some stuff up too. Really, I have no clue and I'm learning on the fly. I recently started experiencing some slow shutdowns and reboots, but I seemd to have fixed that by assigning my "startup disk" within preferences to Mac OS-X 10.11.11. For some reason nothing was selected. Now that this has passed, I'm having iPhoto crash immediately upon opening. It happened a bunch of times, and I figured I'd give "disk utility" a shot. I verified disk and repaired permissions. iPhoto seems to work fine now, so it seems repairing persmissions might have fixed my problem. Does this sound right, or is it just coincidental? My question is whether or not installing a bunch of applications, like MacHeist's, can monkey with persmissions?? Again, I don't understand why. I'm thankful Mac-OS X has a cool tool like this. How often should I fix disk permissions to keep things running smoothly?? Only when I do certain things?? Encounter problems?? Or running every month or whatever as a means of prevention?? Thanks to you Pros for helping me learn in this new world.