Removing metadata from your documents before sending them is important for security, and also sometimes required (at least in Oregon, by Formal Opinion 2011-187). LegalStat Ltd writes about metadata in social media at http://www.legastat.co.uk/site/about_us/legastat_blog/ediscovery_and_social_media_what_do_you_know
The Oregon State Bar provides Law Practice Management Tips for scrubbing metadata from Word and other programs. Mac users of Word should check out http://oregonlawpracticemanagement.com/2012/02/13/scrubbing-metadata-from-word-2011-for-mac/
Microsoft provides information for PC Word users at http://office.microsoft.com/en-us/word-help/find-and-remove-metadata-hidden-information-in-your-legal-documents-HA001077646.aspx
Corel provides information for Word Perfect users http://apps.corel.com/lp/wpox3/4627/Metadata_Removal.pdf