Yes it's a great way of extracting images from Office docs, particularly as corporate clients seem to be so keen on supplying images in a Powerpoint or Word document rather than just sending a zip file!
As far as I know, it only works for newer versions of the Office applications with an 'x' at the end of the filetype though - eg. pptx, docx. But if you open an older file (eg .doc, .ppt) and resave it in the newer format you can then use the same trick.
It also works for the Open Document file format (.odt, .odp).
Cheers,
Phil