tedster - 12:49 am on Sep 26, 2010 (gmt 0)
If you only removed the soft 404 a week ago, you still have a wait ahead of you. I assume those requests now generate a true 404 status, correct?
With a soft 404, the spam backlinks redirect to your home page and their anchor text is counting toward your home page. Google "should" now process the real 404s over the next few weeks, and gradually you will stop ranking for those keywords.