Looks like MtGox switched to use a different anti-ddos service since around June 20th:http://uptime.netcraft.com/up/graph?site=www.mtgox.com
They seem to be using this:http://www.prolexic.com/index.php/why-prolexic/ddos-mitigation-services/
See ACTIVATION VIA DNS REDIRECT.
Requests go to Prolexic first and are then proxied to mtgox servers (minus potential ddos-traffic).
So they seem to really be investing into availability and security. I assume this service does not come cheap and I bet it is more expensive than the hardened blacklotus hosting they used before. (Maybe they are still using Blacklotus but simply put the Prolexic service in front of their setup)