Tim Bray on Metadata:

"If You Collect Metadata By Hand

The most important lesson I've learned, is: Don't try to collect too much. You might, just might, get people, when they're interacting with your intranet, to label their information by project and title; but more than a couple of fields and people will just bypass the process.

This is harder than it looks. When you decide in principle that metadata should be collected, it will develop that many stakeholders have short-lists of the fields they need to make this worthwhile. You can easily end up with a "short" list of a dozen or more fields that constitute the "absolute minimum" that people think you must have. And if you adopt it, you're deadd, because except in special circumstances (e.g. the WSJ), people just will not take the time to do this.

Automatic Metadata

Obviously, there are some metadata items the computer will give you for free: a filename, created/modified dates, who created it, what kind of file (HTML, Excel, PowerPoint), how big it is. These can be handy for search applications and since they're free, you should collect them and make them available."