Had some problems with MySQL replication yesterday. I setup a new slave to join a bunch of existing ones and found that although ‘LOAD DATA FROM MASTER’ worked fine, once it had got an up-to-date copy of the data that was all it ever had. None of the new transactions from the master were processed on the new slave server.
Solution: server-id on the new slave was set to 1 and conflicted with one of the other servers. Doh!