Of course, people shared links with each other before Facebook - but not with quite the same frequency. Facebook gives automatic thumbnail images, descriptive text and titles to links quicker than ever before - and the extent to which people share links appears to me to have skyrocketed.
Facebook's "like" button was another overdue innovation - working along similar lines.
Of course all this sharing is pretty good for the memes that are being shared. They are more numerous and more viral as a result.
Could things be further improved? Yes!
- Image handling is still very primitive. It should not make users press left and right buttons to preview possible images, but rather display them in a gallery. Images should be flippable, mirrorable, editable, and there should be "add your own image" and use shrunken page view options.
- Sucking in the first few lines of text could be improved on too.
Facilitating the sharing of links is a significant contribution to the planet's collective intelligence.