Anyone writing for the web needs to be aware that web content is treated as data.
This applies to all business documents, not just web content. Parts of business documents are identified and filed by search engines, archiving systems and document management systems.
Among many other items, the following parts of your documents are likely to be identified and filed as data:
Humans read your documents as words and ideas, which is how you write them. But applications "read" your documents as bits of data.
Therefore you have to be extremely careful about what information goes where. No more wriggle room.
Otherwise when your document-data is reused, referred to or cited elsewhere, it may not make sense. Some documents will be virtually lost, and web pages won't be found.
This tip is the tip of the proverbial iceberg. Already web sites combine data from other sites (e.g. Google Maps) with other data (e.g. sociological, medical and criminal data). Put a photo on Flickr and you're also uploading camera data including the make and settings, for instance. Several Webstock gurus made this trend abundantly clear.
Mike Riversdale introduces microformats, another ingenious way that Google et al. already use to produce web pages consisting of data that software can identify as such.
And you thought you were just writing words.