Is dropping in on friends or being dropped in on OK with you?

I have this friend and we're fairly close, but she can't imagine anything wrong with just showing up at someone's doorstep without notice. I think it's pretty normal to check with someone first, even family members, before just showing up. I'm told I'm sad and lonely to keep people at such a distance. Am I out of the ordinary here or what? Is it ok with you? Or not?