However, as noted here previously, Apple has since released a foam strip of its own, which it claims is safe to use. Despite the $.90 catalog price, Apple is making the foam pad free to customers that have third party RAM. Apple is also providing the foam pad to RAM vendors to include with their RAM.
However, many PowerBook 3400 users will not need this pad at all. As Apple states: "If you purchased a PowerBook 3400 computer with a serial number that begins with CK712 (or greater) or TY711 (or greater) your PowerBook comes with a modified keyboard that includes a foam gasket and does not require an additional foam gasket (Apple's or a third party's)."
A statement about this should now be in Apple's Portable Computers Discussion board, but I have been unable to access it today, so I could not confirm.