Clearly stackexchange is showing pro-db bias. I'm a huge fan of unstructured data in filesystems as well, that's how the service behind my prototypesapp.com is built.

I also happen to think MySQL-backed websites are the bane of the internet, further testament to the pro-db bias of the average web developer.

A properly built sql store (or, increasingly, nosql) is definitely a necessity for large service. But what is "large"?

I once heard the rule of thumb that a db is necessary when the size of the data you store in it becomes larger than the size of the db code. I kind of like it.