If you're playing a high-level Druid in World of Warcraft and actively use the Moonkin Form to tank, then you might want to check out the Moonkin Tanking Instance thread in the official WoW Forums.

For those who aren't familiar with this Druid form, it grants a 400% armor increase, 150% of level attack power boost as well as other benefits.

The Moonkin Form is a very effective tank in practice with the boosts it gains as well as the ability to still cast balance spells. However, as with all tanks, it cannot survive well without support from both a DPS class and a healing class.

The thread is such very good read that even Blizzard community manager Salthem posted his thoughts on it:

This is a very interesting read. I have not had the pleasure of grouping with a tanking Moonkin myself but I can certainly see that it is perfectly viable. It's an excellent "thinking outside the box" idea and I'm going to go persuade a balance druid friend of mine to help me try this out myself.