Speaker notes are usually somewhat hidden. You can see them if you have the editing window open at the bottom of the slide edit screen, or when you print the notes pages. It is easy to forget that you've entered them.
Nonetheless, they are an integral part of the PPT file. You send the PPT, you send the notes. So be careful in case you use notes to add side comments like "note to self: do not bring up the poor 2008 performance! :-)". A sure guarantee that it will be brought up during the presentation. UPDATE: Akash Bhatia provides a wonderful solution in the comments. I have re-written my post below:
One solution could be to send a PDF version of your docoument. But there is a smart feature in PowerPoint 2007. Hit the Office button, select "prepare" and then click "inspect document". It lets you purge all kind of personal information from your presentation, including presenter notes. Make sure to save your file under a different name before saving.