We always run with 3 tanks, paladin (me) warrior/druid and druid.
It helps avoids wipe situations if I go down (me being MT) due to lag/healer lag/bad timing etc, then there are two other tanks available to pickup my mobs. It has saved us on numerous occasions when one of us has died. I generally make sure that all of us are tanking something too so that the tanking gets spread out.
My main reason for going in with 3 tanks was so that all the good tanks in the guild got to tank together, and we work extremely well like this. If you wanted I could give you examples for how our boss fights usually go.
Having 3 Tanks avoids tank envy, and gets your tanking corps
tanking as a team, at the same time in a 10 man raid instance.
FYI we have a 3 tank, 3 healer, 4 dps as our 'standard' raid group and thus far it's worked very well. (Furthest we've got is Curator).
Good luck to you.
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Samildanach lvl 70 prot 0/49/12
Danathiel lvl 66 Hybrid
Ballin lvl 50 Holy
In the kingdom of the blind, the one-eyed man is king.
http://armory.wow-europe.com/character-sheet.xml?r=Kul+Tiras&n=Samildanach