In 6u10, we changed our policy from "notify before download" to "notify before install". This means that all users who have auto-update enabled (most) will download all of the installer files before even being prompted. Seeing as a great number of users refuse to auto-update, this has caused a huge spike in downloads when 6u12 went out. We're working things out with the server guys, but until we have it completely figured out (with flow control) we'll need to make changes to make sure iftw.exe doesn't download the xml/msi/mst files for all users.