Uber_SEO - 8:28 am on Jun 3, 2011 (gmt 0)
In most cases the robots.txt file has done the correct job - I've seen 99% of traffic to the pages I'm blocking drop off. It's just in some strange cases (presumably where I've got good links coming into page) these URLs are still showing up in the SERPs.
@indyrank - we haven't seen aggregate rankings return to what they were pre-Panda. I've got one specific case where I had a page that wasn't ranking in the top 100, we blocked with a robots.txt, and now that Google has dropped the cache, the page in question is now ranking on the 2nd page for its core term. Pretty random