Yosemite users with Scan Snap -watch out!
Scan Snap users take note!
I've got a mid 2013 MacBook Air (MBA) that was running Mavericks fine. I placed the Yosemite installer onto the MBA by copying the downloaded installer from an iMac onto a USB stick -note I did not create a boot usb etc., this was just a straight copy. I ran the Yosemite installer on the MBA and all seemed to be fine after about three hours of work.
Next, the Fujitsu Scan Snap auto update kicked in and this is where all **** broke lose. The active front window of the installer would constantly blink on and off preventing me from completing its update, but then I realized that the entire system was doing this now, every finder window and every window of all apps. open. I managed to get the installer to run and update the scan snap software ( I think) but now my MBA is in this constant window blinking mode as if one is selecting and then de-selecting the active front window. Reboot / restart did not help. I also noticed that upon reboot / restart I get the black apple boot screen with the apple logo and the progress scroll bar across the bottom-something similar to iOS update and nothing I've seen before on the mac.
Booting into safe mode results in the problem going away, so it looks like I've got to copy my Mavericks back up back to this beast and start over.