im tank squad leader of a pretty average guild , we've killed yoggy on normal but it took us ages!
i have the good fortune to have 1 tank of each of the 4 varieties , we have no MT as such (i scrapped that when i took the job) all of us are very closely geared ilevel wise.
more and more im finding the default situation for me is pally tanks everything , we use the bear if there's a single add to tank that has high damage, or the dk if the add requires high threat.
i would sum up the current tank situation as. Pal+DK have the threat for the job, Pal and bear have the survivability for the job.