After upgrading my iMac with yosemite, the startup takes time. The wallpaper appears first and then desktop icons start appearing one by one. It behaves similarly to a webpage that downloads slowly due to slow internet connection.
iMac, Mac OS X (10.4.11)
Did you try Kappy's suggestion of booting into the Recovery mode and repairing the disk and disk permissions? If that doesn't help the reboot into the Recovery volume and reinstall the system. You should not lose any apps that you have now. The only apps that are replaced are those that come with the system installation like Mail, Safari, Preview, etc.
imac slow startup after updating to yosemite
