Players who have been around for a while will recognize this as an update on Shifting Perspectives: Bear 101, written in February 2010 after the Icecrown Citadel patch had gone live. The spec feels like it's in a weirder place than it was a year ago, consequence of some early improvements on the beta followed by a few unpopular developer decisions. As far as I'm aware, bears are still the least-played tank, and I'm not really optimistic that our numbers are going to rebound as things stand.
As with our earlier 101 guide, I'm addressing this to people with no prior knowledge of the spec who want the tools to become a reasonably competent tank quickly. Readers looking for an extended and mathier version of this article should look for the Feral Bear -- Cataclysm Release guide recently published at Elitist Jerks.