The SEO theory is Google weighs domain trust very heavily in the rankings. If you look at top rankings for some of the spammier stuff (search "viagra pills", for example) the blackhat stuff is always a redirect hosted on someone elses domain name (usually gets there by using an exploit), so right now for "viagra pills" 2,3,4 are:
Code:
pharmacyviagra.da.CX/
topos.buzznet.com/user/journal/89533/
palestinehistory.com/pdf/f/11/Viagra-pills.html
Forget the old buy-viagra-pills-online domains, this stuff will beat it any day. One common SEO tactic also is to create a blogspot (or blogger) domain and make posts sending links to your "real" site.