Those crazy Japanese over at Kodawarisan have already disassembled a MacBook, and have lots of pictures to show.
As has been reported, the hard drive looks relatively easy to remove, even for an end user. This is in contrast to the previous iBooks, where removal of the hard drive was quite the endeavour.
The pricing for an Apple-supplied 80 GB hard drive for the MacBook is attractive, so it still makes sense to get that drive from Apple. However, a user who wishes to use a larger drive or faster 7200 rpm drive can purchase it separately and install it his/herself. I'm not sure how this affects the warranty however.