Quoting a quote as seen on Social Networking Glut = Greater Than Four:
RIESCHEL: We looked at five sites and passed on everything. In '99 everyone got in trouble when maybe 17 companies were all trying to sell pet food online. At Mobius, now if we identify more than four venture-backed start-ups in a sector, we won't bite. There are at least 14 social-networking sites. </blockquote
This one is easy: exactly what I've been saying for quite some time -- social networking is a feature not a business model.