Replication isn't magic, though it can be pretty cool. It's even cooler when it works, and that's what this chapter is all about.PostgreSQL 9 Admin Cookbook
Replication requires understanding, effort, and patience. There are a significant number of points to get right. My emphasis here is on providing simple approaches to get you started, and some clear best practices on operational robustness
Replication is an interesting feature of MySQL that can be used for a variety of purposes. It can help to balance server load across multiple machines, ease backups, provide a workaround for the lack of fulltext search capabilities in InnoDB, and much more.MySQL Admin Cookbook
The PostgreSQL quote warns of a dangerous, difficult, and unexplored path, while the MySQL one is the almost bored remark of someone whose biggest problem is to list how many good things you can do. I guess that being exposed to a given technology for longer time changes one's perception.