Google Blogoscope updates sites previously identified as censored by Google in Germany and France in its Sites Google Censors post. You can see how many pages are shown in Google.com then compare to what's isn't showing at Google Germany or Google France.
The sites are all removed due to national laws in those countries, I believe. Google Blogoscope asks for Google to tell people when material has been removed, in the way they do for copyright reasons. John Battelle and I both asked for the same thing, in the past.
For John's views, check out Google News And China. From me, Got To Censor Search Listings? Why Not Disclose? explains how Google disclosure of copyright-driven removals in the US works, how no disclosure of spam removals is noted and how Google and all search engines have removed material for various reasons and should come up with a way to identify this. My China Blocks Google News -- So Bring On The Disclosure also coves the issue.
By the way, my usual refrain for "Google problems" like these is that they are often "search problems" and so people should also ask what's the situation with Yahoo, MSN and so on. But in this case, it really does look like a Google problem.
I went to Yahoo Germany and Yahoo France and compared to the main Yahoo site, doing some spot checking of how they handle domains where Google has censored. In five checks, I found no or very little differences in the counts that came back -- differences so minor that they likely have to do with factors other than censorship.
Is Google overzealous? Maybe. Or it could be that like too many people, national governments also assume that it's an all-Google world and send censorship requests to Google while overlooking other players like Yahoo.
The exact situation is uncertain because we don't really know how the sites came to be removed from Google. The 2002 Harvard study Localized Google search result exclusions assembled a list of sites heard about, reported about in a few cases and guessed at in others. A follow-up article Censorship of the Internet listed sites working from the Harvard list. Google Blogscope's post was inspired by that follow-up.
In all cases, they give a glimpse into censorship but not the complete picture of all pages removed, nor how and why.Postscript: Also see Seth Finkelstein's long-standing Google Censorship - How It Works page for a look at how Google has implemented censorship on a country-by-country basis in the past.