I rarely answer my main phone anymore. 90% of the time the call I'm getting is from someone either selling something or a bill collector calling the owner of the previous number. Since I have caller ID I can look up the number beforehand and see if I want to answer the call. Unfortunately, many of these calls do not even list a caller name. When this happens I use a service like Phone Number Reporting.
What Phone Number Reporting does for me is gives me the information that other people have listed about the caller. If no one has entered the information and I had the mind rattling experience of getting a telemarketer then I can list the number and what the call was about. For example, today I had an annoying call that woke me up from my slumber. I looked at the caller ID and decided to not answer it because all it listed was a phone number. Then I looked up (800) 448-1103 and came up with a company that I've never even heard of nor was interested in talking with them. Fortunately, I can now just ignore the call and put it on my blocked caller list :)
Another way to use the service is for job searching. A lot of us Internet workers use places like Craigslist and The Telecommute Resource to search for jobs. Some companies refuse to leave information about who they are so it is hard to tell the difference between a scammer and a real company. With this tool you can see if the job is another scam out there by just seeing if the number is listed. What would be really convenient is if they merged with a phone book directory and a cross search could be done. That would be really handy.