ANY prices in ANY book are going to be inaccurate. If you are buying or selling you need to research the market before you make a decision.
I couldn't agree more. Most of the auction sites have archives to review recent activity and prices realized.
The Black Book is the last book I would recommend anyone using for US paper money. In fact, I would not recommend it at all. Friedberg and Krause-Lemke have more detail on varieties. I also find it difficult to trust a book that states that Nationals were printed by the Government Printing Office. (The Black Book really says that.)
The way I look at it: Who wants any book when you have the internet? Books don't get updated like the internet does. Heres an eBay example of why books can help you to go wrong and sound like you don't know what you're talking about: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180729222813&ssPageName=ADME:X:RTQ:US:1123
Catalog values are nothing more than a guide. Sometimes I purchase a note for more than the catalog value, and other times I purchase a note for less than the catalog value. So, on average, it is probably a decent guide.