What do you do with cell phone reverse lookup directories?

What have you done with the information you have retrieved from cell phone reverse lookup directories? I have seen they are becoming more and more popular as a dot com business, but I do not understand why. Are there really that many stalkers, prank callers and bad telemarketers out there that we really need this directory for our cell phone numbers, as well now? I do not understand what the big deal is with these new directories, and I feel like they may just be a big waste of my time and money. What have you used them for and have they worked? Are they worth the internet space they are taking up?