www.3M.com/feet
you can request a free sample package of 3M rubber feet, which will include some white feet that you can replace all four of your 'book's feet with. (click the "contact us" link to the left, and make the request on the form). these are better than the stock feet, because they elevate your ibook a few milimeters higher (better ventilation), and have better adhesive. personally, when i got my free replacements from 3M a few years ago, i just superglued them on, so you might want to do the same.
- Ptrix