It's a common geo-rant (thanks AGI'09) that metadata cause alternatively boredom or angst among geo-geeks - why? because we know our data, our professional audience does too, but our wider audience does not. In other words, if we don't write metadata, no-one else will understand the context later on. I found a clear example, when I mapped Captain Cook's ships logs a while ago, and posted on ArcGIS Online beta: