Glad to see I'm not the only one in Raleigh experiencing this issue. Have 2 month old 3GS with iOS 5.0.1. Started seeing the Kings Grant location this past week. Seem to get this problem when connected to my WiFi at home. When I'm driving it corrects itself. I'll have to see what happens when I'm connected to other WiFi spots at work and around town. Decided to check my wife's phone and see that it's having the same issue. However, my sons iPad has the correct location on the Maps app using the same WiFi as our 2 phones.
Another post in a seperate discussion pointed me to a site that is used by Apple. http://www.skyhookwireless.com/howitworks/submit_ap.php
I used the form to provide the lat, long coordinates of my router. We'll see if it helps.