The slides for the three major presentations I did for the 2002 O'Reilly Open Source Convention are now on-line. They are, in order, "MySQL Optimization" (a 3-hour talk), "MySQL Backup and Recovery" (a 45 minute talk), and "Managing MySQL Replication" (90 minutes). They are also listed on my personal MySQL page.
Wrapping XML-RPC in the Jabber protocol. Use Jabber as an XML-RPC gateway between processes. The requests/responses are completely async. You can do the same with SOAP over Jabber.
Publish/subscribe systems built on top of Jabber. All the pieces are there, it's just a matter of assembling them.
Weblogs.com has a SOAP interface for subscriptions. So you can use Jabber to tell you when a weblog is updated.