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I've had some 20 sites -30'ed. The penalty seems to have been replaced by -60. All sites were manually checked by G the previous day. I've also helped others check their logs and G employees were lurking on their sites 1 or 2 days before the drop. I have not seen an automatic -30 since December 06 but it may be still possible.
My sites were mainly thin affiliates so I understand the penalty but in my latest case the site didn't have any affiliate content so the main reason for penalty remains unknown. Looking at the latest -60 penalties it seems you don't have to be a thin affiliate, thin is enough. Mini sites with very little content can be dropped even though the 10 links and some text they have are very useful for visitors.
[edited by: tedster at 4:47 am (utc) on Dec. 20, 2007]