The infinite scrollbar

It's somewhat annoying when sites decide to show, say, the first 20 items of a list on a web page and to get more you have to find the "next" button.  It's nicer to bring up a list you can scroll through.  As you scroll, the size and location of the scroll bar will tell you how much you've got left.

Except when it won't.  Some sites -- particularly social sites, it seems -- will give you a scrolling list, but when you get near the bottom, they hit the server and bring in more items.  Suddenly your scroll bar gets smaller and the space below it grows.  After a while you realize that no matter how much farther you scroll, there will still be some left.  But by then you're hooked.  Just one more page ...

Technically, it's not a bad call.  Browsers can handle pretty big scrolling lists these days, but they probably wouldn't deal well with the full list of, say, hundreds of thousands or millions.  Bringing items in on demand is a nice compromise.  Chances are the human doing the scrolling will grow bored long before the browser's memory limits are seriously tested, and if not it can always throw out items from the top that are now well out of sight.  Score one for AJAX.

Psychologically it's pretty clever, too.  The nice large scrollbar at the beginning says "Come on in!  Just a little bit to look at here.  Won't take too long."  As noted, by the time you see what's really going on, you're drawn in.

Overall, I'm not sure I have a strong feeling about this style of widget.  I guess the convenience outweighs the subtle feeling I've been played.  But not by a lot.