The History of Tremendous Wastes of Time
CNET has posted a list of the Top Ten Web fads. The list might cause you to smile or cringe--regardless, you get the point.
Some of my "favorites" are on here, like the Mahir page and All Your Base as well as a few I was indifferent to (Ellen Fleiss, Hampsterdance) or disliked from the beginning (Dancing Baby, Hot or Not). One or two of my favorites didn't make the cut, like the Peep Research fad and Y2Khai.
On a related subject, you could probably do a similar list of faddish "must check" webpages, the kind of thing that you'd make your "start page" for a few weeks or months right after you see it for the first time, then never visit again after it gets tired. I'm thinking of sources of daily amusement like the Cruel Site of the Day or Something Awful.
Then there are those pages you send to friends, bookmark, and forget about until you rediscover them much later while trying to clear out your bookmarks. A few of mine: BIBLE DOCTRINE NEWS, Scamorama, and my favorite, Khaaan!
Seriously, that one's nowhere near as bad as You're the man now dog.com.