Some webpages (dropbox, evernote etc) will opt out your accounts if you aren't keep visiting their pages for a while, its ok for me since the safety is always important. But since I upgraded to Yosemite, safari cannot stay logged in anymore even if I visit these webpages every five minutes, I still need to manually type in my account and password every time. It's particularly annoying since 1password extension no longer works on Yosemite.