5. AT&T (at least when I've dealt with them in their datacenters) does not support BGP community strings for null routing (or any strings for that matter :) Think about that for a second. To stop an attack Register.com would need to call AT&T and request a filter/null route. Since AT&T operations is based in Singapore (again this was last time I dealt with them) I'm sure getting those filters/routes in probably doesn't happen nearly fast enough. I have heard that AT&T is currently in the process of setting up communities- maybe someone who knows more could comment.
Well, this is not exactly true. AT&T does support BGP communities, although their communities aren't all that powerful, IMO. To my knowledge, you are correct when you say that they do not support any null-routing capabilities. I would love to find out the procedure and string required to request/implement null routing via a community. For those who would like to see AT&T's official guide, it can be found at: http://www.onesc.net/communities/as7018 charles