I just came across a blog post via Twitter that was a dialog between a Googler and others at WebmasterWorld.  The Googler made this claim:

"...I've personally been working on it [spam issue] for over a year. The central issue is that it's very difficult to make changes that sacrifice "on-topic-ness" for "good-ness" that don't make the results in general worse. You can expect some big changes here very shortly though."

More on this later - I'm in a conference at OMS San Diego on Social Media.  Great stuff to start sharing with my clients!

Here's a link to the original post: http://www.webmasterworld.com/google/4263013.htm