I use honey to prime. I have been using 1/2 cup to prime 5 gallons but I am going to try just a bit more honey than that next batch.
Added info:
Honey should NOT be boiled.
I bring 2 cups of water to a boil, measure off the honey in my measuring cup, remove pot from heat, add honey and stir it up until it is 1 consistency then add that to my 5 gallons, gently stir that into the beer and then bottle.
In many recipes that call for using honey they talk about it in lbs. The ratio is 1 pound = 1 cup in brewing.
Honey is 74-80% fermentable, depending on brand/type.