econman - 3:32 pm on Mar 18, 2011 (gmt 0)
I'd 410 all of the low quality, largely scraped pages. This will have the effect of immediately improving your good to bad ratio. And, it puts you in a stronger position to understand what's happening with your site, and to make additional improvements which will be necessary in order to survive the changes we can anticipate over the next year.
Google has indicated this Panda update is just the beginning of a year's worth of changes; for the first time they are attempting to pay attention to quality and not just relevance; they think the update has been successful; they will use their "machine learning" approach in an effort to expand the reach and improve the precision, and there is every reason to assume they will make other changes which put more emphasis on quality in the future.
Some people have been complaining that Google didn't give us enough warning. Perhaps that's true, but we should all act as if we have been warned about even more dramatic changes ahead.
Panda represented the first little baby steps for a new approach to ranking results -- intended to affect 12% of all queries, intended to push down low quality content, and it's only been rolled out in the US.
Over the next year or two, it seems reasonable to anticipate:
a. many more queries will be affected.
b. they will try to detect and boost high quality content, and/or push down mediocre content.