I don't use Microsoft programs myself, but I don't live in a vacuum, so I am aware that other people not only use them but also send around files in Microsoft-proprietary formats.
If you don't already know that sending Word files as attachments is not a good idea, you should read "MS-Word is Not a document exchange format" by Jeff Goldberg, or (much shorter) "Avoid E-Mail Attachments, Especially Microsoft Word" by Neal McBurnett. Both Goldberg and McBurnett point out the risks of embarassment (or worse) from distributing Word files, or files in other formats created from them, as the Department of Justice, British prime minister Tony Blair, and Danish prime minister Anders Fogh Rasmussen have discovered.
The U.S. National Security Agency (NSA) has published detailed instructions in Redacting with Confidence: How to Safely Publish Sanitized Reports Converted From Word to PDF (Report # I333-015R-2005, PDF, 665 KB). They recommend against releasing even a sanitized Word document; the last step should be conversion to PDF. Some excerpts:
Although the focus [in the report] is on MS Word, the general guidance applies to other word processors and office tools, such as WordPerfect, PowerPoint, Excel, Star Office, etc.
This document does not address all the issues that can arise when distributing or downgrading original document formats such as MS Word or MS PowerPoint. Using original source formats, such as MS Word, for downgrading can entail exceptional risks; the lengthy and complicated procedures for mitigating such risks are outside the scope of this note.
As numerous people have learned to their chagrin, merely converting an MS Word document to PDF does not remove all metadata automatically. In addition, Adobe Distiller and the PDFMaker Add-in to MS Word (the most common way to convert) convert much of the layering complexity from one format to the next. For example, images placed on top of text in MS Word will be copied verbatim to PDF with the same layout.