For a combat druid thorn body is very usefull.
Any creature striking you with a melee weapon, an unarmed strike, or a natural weapon takes 1d6 points of piercing damage +1 point per caster level (maximum +15)
This is very good, adictional free damage.
Creatures that successfully grapple you take 2d6 points of piercing damage +1 point per caster level (maximum +15)
Good, i think this works also if you grapple.
In addition, your natural attacks and unarmed strikes deal an additional 1d6 points of piercing damage.
For me this is blue for a combat druid and green for a caster