At the beginning of February I added meta noindex to the tags pages (keyword pages won’t be indexed in Google) to seo bugz.
After Google removed the tags pages from his index (site:seobugz.com), traffic from Google jumped by 300%.
Maybe because the inside PageRank doesn’t split to so many pages and other sites rank better.
Another method to make your tags/search pages not appear in Google is to use robots.txt:
User-agent: *
Disallow: /tag
More about robots.txt and tag indexing read on capslock.ro (in romanian).
I created seobugz.com tool for beginners in SEO or if you just want to get a fast overview of a website optimization.
SEO Bugz is an automated script that will parse your website analyze and give you a full report about any SEO mistakes that you have made.
). (currently working to tweak a bit the category privacy module).