A few interesting MySQL replication scenarios: 

Encrypted WAN Replication:
A company with mission-critical database services wanted real-time WAN backup of MySQL database. I setup remote, ssh-encrypted MySQL replications across WAN for real-time backup of SQL database. System supports “catch-up” replication in case network is slow or down.  Allows client to recover to any moment in time if main server goes down.

Split Replication with Blackhole tables: 
A company had setup a DB with thousands of tables in it and a gigantic legacy system that needed to be overhauled. The company  needed to replicate part of the DB to other systems, BUT some of the queries on the master referenced tables that were not needed on the slaves. Setup replication of a few tables using suitable my.cnf configuration settings and blackhole tables to avoid errors that would have stopped replication. 

MySQL 5.0 to 5.X replication with Binary Log Cron-clearing
A company with a legacy system was in the process of migrating and needed replication between the old and new systems. So much data was written per unit time that unpurged binary logs threatened to fill the disk systems. Setup cron bash scripts to check to see where the 5.1 systems were at in replication and cleared out 5.0 system logs periodically.