I had a very odd experience with Apple's most advanced OS - OSX 10.10.3, today. It started when I wanted to share a few photos with Photos app. I opened my Macbook's lid to wake it and clicked on Photos app icon. It bounced and took longer than usual to open. When it opened I noticed that the Photos app was missing the small album icons and some other UI elements. It was all sluggish, even tho Activity Monitor didn't show any CPU load at all. I opened App Store and saw that it also had some missing UI elements - forward, backward buttons and Feature, Top Charts etc icons. Restarted my mac but it didn't fix the issue. Searched around some more and tried safe mode. It seemed to fix the UI elements issues. So I restarted again but now I was unable to boot at all. The loading bar (during boot) below Apple logo was moving very slowly and it stopped with the circle icon with diagonal line crossing it. After that I was even unable to boot into safe mode. PRAM reset didn't do anything. Disk utility in recovery showed that the disk is ok and fixing permissions didn't help either. The only thing that was left to do was to reinstall OSX without erasing the drive and now everything seems to be working again like nothing happened. Have anybody else experienced similar odd issues with Yosemite/OSX?