Returning to my original question, there is quite a good article on 15 representative uses of PHP here. It begins with the database applications that I began with, but then goes on to list some of the uses that James mentioned and that Daniel alluded to.

Adrian has addressed more the question of good practices in learning, and Daniel has touched on that also. I wish that there were more comments along those lines, here and in other forums. It's so helpful to have the encouragement of other's people's example and the benefits of their experience.

Gentlemen, thank you again.