Define accurate. My ISP lists me as connected to a Redback which is 73 miles away. (Life in a small town.) When I want privacy, or to access difficult servers, I can browse via a shell account which is hosted from a location across the continent. On the whole howerver IP location will tell you what region of the country most of your logins are from. Just make sure the users know the data can't distinquish between city vs rural, or between nearby cities.