Anyway, I'm not saying "never use MySQL for mail users" (though, I think the percentage of deployments where it makes sense is closer to none than it is to one), I'm just trying to make the point that MySQL is, in some folks minds, a magical solution to performance problems. Often, it not only introduces needless complexity, it won't even improve performance. It's a classic example of "when all you have is a hammer, everything starts to look like a nail". MySQL is a very fine hammer. It just isn't the right tool for every job.
The article we're talking about is another case where a little knowledge is a dangerous thing. A desktop app serving one user with a tiny data set (as I understand it, we're talking about the metadata for a person's music collection) is exactly the right workload for SQLite. I'd be shocked if a naive port to MySQL were faster (though they acknowledge that there's room for query optimization), and not at all surprised if it were slower. And, I know it'll require more memory and disk space for the same working set.
Shouldn't user groups give a bit more accountability there?