I've never been with a company that didn't have serious problems with MySQL replication. At least once a month master-master replication breaks horribly and must be manually fixed; often by having to delete and remove data. MySQL replication half-works at best.
I look forward to the day that happens at my work then :)
To be clear, our master/master replication is strictly read-only at one site and read-write at the other site, and never read-write simultaneously. We have yet to see issues in production under fairly hefty write load, and we've failed over numerous times, and back again. But it's only been 10 months or so.
