I bought a 1999 guide book for NYC. Other than the obvious change circa September 2001, I have found a lot of little things that are incorrect or wrong. It does a decent job of getting me around via it's maps and giving me a general feel for the neighbourhoods I am in, but everything else is out of date and showing way less of a price. Even the subway and trains have changed in a few places.

I have had some success with just printing pages off the web and winging the rest. For Hong Kong, Paris and Brussels, I was able to print off a city map (or pick one up for free at a hotel), a metro / subway map and 6 or 8 pages from the lonelyplanet.com, fodors.com or similar travel website and get by fine. For restaurants I just walked around and looked at menus and how many people were inside - busy is good. For hotels, I researched it all online.

Greg