The MyTrackables section of the website is rendering strangely (seems to be missing its CSS in many places), but if you dig through it and try to actually download a set of trackables you'll only get "The requested page could not be found."
This is something of a major crisis, and the reason why there will always be limits to what we're willing to do with Vuforia as long as you won't give us the ability to make our own trackables without depending on a web service. :/
Please fix it fast. Thank you in advance.