Geocities now uses these instead of
pop-up ads. Basically they are a little
square of
advertising that stays in the upper-right of your
browser window. These forms of advertising can be easily
closed with two clicks in the same place, one to
minimise the window a-la
Winamp, which also changes the
button to the familiar
"X" close one. Unfortunately the square will re-appear once you go to a different window, so I'm not sure whether it's worthwhile to close them or not.
I'm still not sure whether
I prefer pop-ups or the new and
"improved" ad-squares.