Math online

Places to find math:

Type of site	Examples	Is it useful as a course?	Is it useful as a reference?	Is it fun?
Video lectures	Khan Academy, MIT OpenCourseWare, YouTube	Yes	No	Some
Q&A/social	MathOverflow, StackExchange	No	No	Some
Online books	Applied Topology and Geometry, Hatcher's topology book	Yes	Yes	Some
Lecture notes	Online lecture notes	No	No	No
Encyclopedias	Wikipedia, PlanetMath, Wolfram MathWorld	No	Yes	No

Will there be time when everybody keeps his stuff at his own site and all of these "communities", aggregators, middlemen die out?