According to a Business Week article the French are the keenest bloggers in terms of number of blogs as a percent of the total population - 4.9%. It's 1.4% for the British, 3.5% for the Dutch and 0.2% for the Germans. Even American bloggers only make up 3% of the US population.
Loic Le Meur, founder of Ublog.com says it's because "French people love to tell everyone exactly what's on their minds - far more than Germans, for example." I would add to this that they also like to have a really good argument about it too, and the comments on a blog provide an excellent venue for that.
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Ton Zylstra (Interdependent Thoughts weblog, http://www.zylstra.org/blog) sent me this comment which he was not able to post (I'm sorry, I still haven't been able to fix the problem that has led to my disabling the comments):
Those numbers come from my partner Elmine (http://elmine.wijnia.com/ ) who added them to the wiki of Loïc when he asked numbers for the European blogosphere. She took the estimated totals in those wiki-pages for all countries mentioned and divided them by the number of inhabitants (those numbers taken from the CIA Factbook website) So all percentages are speculative at best, as the number of blogs in any country remains speculative (France's position is due to 2.4 million blogs at Skyblog, a contested figure e.g.). Also note that this list only covers European countries, not what's happening in Asia for instance.
You can find the whole list here:
http://www.socialtext.net/loicwiki/index.cgi?summary_page