Raw Sockets
Steve Gibson predicted that Windows XP would basically destroy the Internet thanks to it's inclusion of raw socket support.
"The threat represented by Microsoft's forthcoming Windows XP operating system, with its confirmed ability to easily generate malicious Internet traffic ? for NO good reason ? can not be overstated. The proper executives within Microsoft MUST be reached with this message so that those plans can be reviewed in light of the potential for their system's massive abuse of the inherently trusting Internet."
Remember that? Remember the folks saying that Y2K was going to be the end of the world?