From what I'm seeing, the following three sites look exactly the same. I created a profile on only the first one, but I see I now have profiles on each of them. What is the difference between the sites? Is there any case when I should prefer one over another?
Stackoverflow careers 2.0
Joel on software careers
Server fault Careers
From Joels blog, (note the links)
According to whois, joelonsoftware.com is owned by fogcreek.com
From http://www.joelonsoftware.com/items/2008/04/16.html, he is the co-founder of SO. So that site may be part of the SO network, or something he uses for testing.
For the others you listed, most likely any SO domain using the
The preferred site to use is http://careers.stackoverflow.com