Bates-stamping is incredibly useful for legal professionals. If you own the Professional version of Acrobat you can easily stamp a PDF document (or a batch of PDFs) with text, or sequential numbers. I put together a handy PDF guide that contains the step-by-step instructions for how to do this.
The guide won't help for Acrobat X Professional, because the initial steps are under different menus than the prior version. However, it should work for Acrobat 8 Professional. Remember, that Acrobat Standard does not have the bates-stamp feature.