Tim Bray - No Database!?:

"I like the semantics of the Unix filesystem, and I also really like the fact that whether you’re talking ufs, ext3, zfs, or whatever, this is some of the world’s most thoroughly-debugged and battle-hardened code. Also, most modern operating systems are really quite clever at noticing when part of the filesystem is getting hammered and caching the whole thing in memory, so you may never go near a disk.

I’m not religious—I’ve deployed runtime databases where I’ve had to. But there is a psychology out there in our profession,which says: if you have data that you want to store and retrieve, that means you need a database. But sometimes you don’t. And sometimes you come out ahead on one or both of the less-work and runs-fast metrics by not having one."