= End of Life
= no more updates including for security and is considered "dead"
= no more 3rd-party software updates (security or otherwise)
= no more updates for your anti-virus definition files
= problems with compliance with PCI DSS, HIPAA and who knows that else.
= even more companies getting serious about moving off XP
= EOL for IE8
= bliss for developers
= total death spiral for XP