Like adverts and sidebars could page content adapt to match the reader?

Like adverts and sidebars could page content adapt to match the reader?

For a long time web designers and content authors have been able to change what’s displayed on a page depending on who’s viewing it. However this is normally restricted to adverts and sidebars. Soon we could see that actual page contents adapting to suit the reader as well. When you visit a webpage does it look the same each time you view it? Does it look the same as when your friend views it?