Much as I loathe Microsquish's Word, it does allow you to insert into a header or footer the automated text "Page X of Y."
When using InDesign, it's easy to set up the "Page X" part on a master page. But is there any placeholder character for the Y? That is, it will count the number of pages in the document, either in an absolute or a relative-to-the-section fashion? Every now and again I narrowly miss sending out something with a footer which reads "Page 4 of 3," and I would love to know if there's some way around that.