Metadata is a hot topic in the legal field right now -- heck, it's a hot topic in a lot of fields; this article on Document Security 101 shows how a little bit of information left in the metadata can embarrass or cause harm. And it's usually not the technology that's causing the problem -- it's more likely to be user error.
Dennis Kennedy, Evan Schaeffer and I discuss this very issue this month in our Thinking E-Discovery Column, Mining the Value from Metadata.
Our article talks mostly about making sure you rid unwanted metadata from your Word documents; check out Clean Up Your PDFs to learn that even if you do the right things with Word, you're still not home free if your PDFs contain metadata.