This article is from the Macintosh for sale FAQ, by Elliotte Rusty Harold firstname.lastname@example.org with numerous contributions by others.
Almost nothing. It's certainly worth less than the cost of
distributing a for sale message around the world on Usenet. If the
software is the current version AND includes all original master
disks and manuals AND a notarized letter transferring ownership
from the original purchaser to the new owner, then it's worth
about half of the current mail-order or educational discount price,
whichever is lower. Especially note that software left on a hard
disk when a computer is sold adds NOTHING to the value of the
system. The buyer can pirate payware and download shareware
just as easily as the seller.