I think the most useful thing to have on paper as you wander around someplace is a good map or map book. Mobile phone maps with GPS just aren't that reliable world wide yet, when they get there, then maybe the map won't be necessary.

I do tend to buy one guidebook to learn about a tiotally new place and my first decision filter is publication date. Guidebook companies seem to have learned that many of us check this and have become expert in hiding the copyright date somewhere obscure. If I can't find a date, I don't buy.