del.icio.us/popular is pointing to some random list of the 100 best SF Books EVER!.
The problem with this or any 100 best list is that the listing and ordering is totally random. Many of the books listed here are certainly among the 100 best SF books, but their relative rankings are totally out of whack. Some are darn good, but don't belong on a 100 best list. Others are classic SF, but not in the top 10, or much better than the lower 50.
All of which leads me to conclude that the world's best (and perhaps only) algorithm for creating a 100 best list is this: take a whole mess of candidates, throw them into a blender, do not put the top on, and see what sticks to the wall when you turn it on. Order the resulting mess from top to bottom, left to right.