Essential oils in the garden?

I'm curious if anyone here has tried essential oils like tea tree, peppermint, eucalyptus, or Neem. I have experience with products that contain them (especially Neem, it's in so many organic incesticides) but I've never used the essential oil versions.

I recently came across a recipe that calls for 4-8 drops of essential oil to one gallon of water. The author says to shake it vigorously and spray. Would love to hear your first hand experience working with essential oils in the garden.

I've only used Neem so far but have seen quite several people talking about using Dr Bronner's peppermint with great success to get rid of pests. I mix my neem with protekt which helps emulsify the oil and provides some silica too.