(formerly)tangentmind.org

Once, on easter, my dog ate my chocolate rabbit. I was pissed, understandably, but it was my fault for leaving the chocolate on the floor. Chocolate is poisonous to dogs in sufficient quantities, however, and so I was thinking about how dangerous that chocolate bunny could have been to her.

http://www.dogownersdigest.com/news/library/chocolate-dog-poisoning.shtml
"Chocolate contains theobromine. A naturally occurring stimulant found in the cocoa bean, theobromine increases urination and affects the central nervous system as well as heart muscle. While amounts vary by type of chocolate, it's the theobromine that is poisonous to dogs."

It can cause:
Hyper excitability
Hyper irritability
Increased heart rate
Restlessness
Increased urination
Muscle tremors
Vomiting
Diarrhea
Possibly death

Each different kind of chocolate has a different amount of theobromine.
All numbers are mg per ounce.
White chocolate: 1 mg
hot chocolate: 12 mg
milk chocolate: 60 mg
semi-sweet chocolate: 260 mg
Baking Chocolate: 450 mg

The chocolate bunny falls under the milk chocolate category so she could probably eaten about 25 ounces of milk chocolate before it become truly toxic. I don't doubt that it gave her digestive issues. She used to have a very sensity stomach. I'm not sure how many ounces the bunny was, but it wasn't too small. I imagine it was probably less than that. 6 maybe?