Hmmm... as noted elsewhere here, the question of whether it is ethical to look for metadata in a document e-mailed among opposing counsel has split the bar associations. Pennsylvania recently issued opinion 2007-500 (not available on line, but at 30 Pa. Law. 46 and on westlaw). After surveying those opinions, the committee concluded that "it woudl be difficult to establish a rule applicable in all circumstances and that consequently the final determination of how to address the inadvertent disclosure of metadata should be left to the individual attorney and his or her analysis of the applicable facts."
Pretty wild, what is happening on this point, with some states saying it's dishonest, some saying it's not, and Pennsylvania saying "it depends."