I remember as a kid going all the way to Washington, D.C. to visit the Smithsonian Museum on a two-week family road trip (shudder), and the only thing I walked out of the gift shop/bookstore with was a copy of the newest Overstreet Comic Book Price Guide. Not that I really cared about how much any of my comics were supposedly worth -- I never planned on selling them anyway -- but the draw for me was the tons of advertisements for various comic shops around the country. I spent part of the trip back to Dallas circling all the ones I needed to order comics or catalogs from.
Nowadays I'm really out of touch with the segment of fandom that does care about how much their comics are worth, and I haven't seen one of the guides in ages. But I do like the 1970's Conan #1 cover recreation that John Romita Jr. provided for the Hero Initiative's limited edition version of the guide. They'll have 500 copies of them in San Diego this year for $35, with the full cover price going to the Hero Initiative.