Jumping in head first

Your mother always told you to look before you leap. No diving in the shallow end.

Well, as I have a bunch of sites I want to review, I figure I should get some sort of 'checklist' going as to what is a good GIS & Web Map Application. I don't want to get into scoring these things on a scale of 1 to 100 or anything, but a checklist is in order.

Submit your thoughts or point me in the direction of what you think makes a great web mapping application.