Back in April I started a duplicate content test. The Google Webmaster team had said at Search Engine Strategies NY that if you had one domain that was a .com, and another one with a specific country domain (say a .ca), then the one with the specific country domain would rank better for searches done in that country. They also said that you wouldn't need to worry about duplicate content in this situation - that they would understand that you were targeting the country in question. So I set up slicksurface.ca as a separate site, and waited...
Well, after 5 months not much has happened. Slicksurface.ca only managed to get 24 pages indexed at both google.com and the google.ca, and most of them are label pages from the blog or Flash movies. It did a little better at Yahoo!, but this was really a Google test since it was the GWT's comments that started the test. We didn't do link building for the domain - there's a good chance that would have changed things had we gotten links for slicksurface.ca from Canadian sites.
So the test is over and we're 301ing slicksurface.ca back to slicksurface.com.
It should be noted that this now destroys all my faith in what the "experts at Google" say about how Google works. Matt Cutts was wrong when he said you should do major additions to sites in a staged manner. I added over 166,000 pages to slicksurface.com all at once without any obvious detriment to the site. Google indexed everything and is sending us a fair amount of traffic as a result. And now the GWT is wrong about country TLDs getting picked up for use in the particular country.