MySQL Replication Failure Causes

One of the reasons why MySQL replication failure happens:
1). MySQL Replication user password length should be 16 characters in length.(Need to check  for Version)
Replication always looks for USE <database>; command before any DDL statements or DML statements.

Eg:

Connecting to mysql as root user, insert as below

insert into <database_name>.<table_name> values ;
This entry will be recorded in mysql bin log as blank database and since the slave server does not have any such database, the transaction will fail.

Slave replication always looks for USE statement;

http://dev.mysql.com/doc/refman/5.0/en/replication-options-slave.html#option_mysqld_replicate-do-db
http://www.mysqlperformanceblog.com/2009/05/14/why-mysqls-binlog-do-db-option-is-dangerous/
http://stackoverflow.com/questions/5174327/mysql-replication-changes-not-being-sent

MySQL Replication How To:
http://aciddrop.com/2008/01/10/step-by-step-how-to-setup-mysql-database-replication/
http://dba.stackexchange.com/questions/31230/master-master-replication-not-working