Tonearm - 8:25 am on Sep 17, 2013 (gmt 0)
I don't think keeping two copies of the site running simultaneously is a good option for me. The site is database-driven and I don't think it's possible to keep two copies of the database in sync without opening a can of worms. Am I asking for trouble with Google if I shut down the old site when I update my DNS? People will be unable to reach the site until their DNS is updated but I don't think there is another good option for me.
As for vetting the IP address, it's easy to check for blacklists, but is there a good technique to check for other types of spam such as that which FranticFish's agency ran into? That seems tricky.