I don't know what TTL is so I'm not sure if you have covered one point which caused me quite a problem when I moved from a static html website to openacs on a new server.
All users going to http://mysite.com were OK (no www. subdomain).
A number of users for certain ISPs going to http://www.mysite.com were going to the old website.
The reason was: I never asked the old hosting company to delete their www.mysite.com subdomain in their DNS and for some reason some ISPs were picking up the old record ever though the mysite.com domain was now being handled by the new hosting company and they had a www. subdomain defined. Once I got the old subdomain deleted everything was jake.
