Peter Saint-Andre, Executive Director of the Jabber Software Foundation says:
We have migrated jabber.org server to [ejabberd], because we were looking for an Open Source server that could meet our scalability needs. From our knowledge of existing large deployments (e.g., Gizmo Project and MXiT) as well as test results posted on the Internet, that meant ejabberd.
We decided the migration to ejabberd to benefit from improved stability, full XMPP compliance, support for a wider range of XMPP extensions (e.g., pubsub), and a more frequently maintained codebase.
Check it by yourself on Jabber.org Status Page