I was sent this in relation to something else, but it has some
thought-provoking data on it: 

  http://www.siteadvisor.com/studies/map_malweb_mar2007.html

It shows the risk of malware distribution sorted by top-level domain.
It shows that ".au" has the almost the lowest risk, ranging up to the
highest risk being in Tokelau -- which offers unrestricted domain
registrations for free.

kim