There's some new data concerning who uses the online versus print version of the Yellow Pages.  Not surprisingly, the split has more to do with age than anything else, with younger searchers under 44 preferring to turn first to online sources.  It seems older demographics continue to use the print book.  So if your target audience is made up of younger people, then you must have an online presence in the search engines and online directories.  And if your audience skews older, you'll still need an ad campaign in the print book.