Google Spam Algorithm Version 3.0 Launches Today
Matt Cutts explained that 2.0 was targeting specifically spammy sites, while 3.0 targets more spammy queries. So the algorithm looks more at the query versus looking at the site.
It looks at search queries to find spammy sites:
Reminder, this will look specifically spammy queries, such as terms like [payday loans], [casinos], [viagra] and other forms of highly spammy queries.