If you haven’t tried this before, try typing the following line into a Google search box:
This should bring back a list of every PowerPoint file Google has found on the web. Results like this show up in regular searches, but the filetype command easily narrows things down.
Steve’s right that it’s amazing what you can find. Here are a few examples that bring up some revealing information where the filetype is combined with a word (or words) included in the indexed file:
filetype:xls confidential (marking something as confidential suddenly makes it less so)
filetype:pdf predictions (refine this a bit further for your industry)
filetype:ppt jobs reorganization (lots of stressful presentations of shifting org-charts here)
They can get much more damaging than this.