I generally agree with Mika, Jeff and others about this sort of copy "protection". There is, however, a particular use case where I have used it successfully and, I think, with justification.

That usage was on a site where I was explicitly providing an alternative (and accessible) means for a user to download content, and that alternative produced a much better finished product than the standard right-click or print menu.

This meant that, far from getting complaints about an inability to download, I got compliments as to how my downloads were so much better to look at than downloads these users had seen before.