My first thought when I saw this Free Reverse Phone Lookup service was 'thank Heavens that I'm not based in the US!' The idea is that type in a US area code and number and it'll tell you who phoned you. All well and good, but they also have a listing of recent lookups. You can then simply click on the number and you've got the person's name, and address, together with other technical details about the number - landline, service provider, exchange and so on. Oh yes, and a handy little Google map of how to get to their front door.
While I appreciate that this information is all in the public domain, and I presume that if you're in the US you can choose to be removed from any directories, it would still worry me that this data is just flying around out there for anyone to find and potentially make use of. If this company just provided the service and you provided the number I'd be happier, but with that element... I wouldn't be happy if my number was included in their random list.