The need to change designs every 6 months to a year.
I hate it when random things get moved on a website for no reason. Youtube was the worst offender for a while. Every now and then, a bunch of stuff got moved around and changed, so you'd have to re-figure out how to do everything again. Also, some sites love to take buttons and shove them in menus, so you get to a page and think you're going insane, because you can't find the button you clicked on 1000 times.