If you're just going to do selective paragraphing, you're not
going to get the rest of the story. 
Quick Guide for Theobromine levels in different types of
chocolate:
From The Merck Veterinary Manual, 8th ed
# Unsweetened (Baker's) chocolate = 390-450 mg Theobromine per oz
chocolate
# Milk chocolate = 44-60 mg Theobromine per oz chocolate
Semi-sweet is a bit less than half of the Theobromine content as
Baker's chocolate.
How much is too much?
The toxic dose of Theobromine (and caffeine) for pets is
100-200mg/kg. (1 kiliogram = 2.2 pounds). However, various reports
by the ASPCA (American Society for the Prevention of Cruelty to
Animals) have noted problems at doses much lower than this - i.e.
20mg/kg.
Translated to a "typical" scenario, and using the 20mg/kg as a
measure of "problems can be seen at this level of ingestion", a 50
pound dog would have to consume 9 ounces (+/-) of milk chocolate to
consume the 20mg/kg amount of Theobromine. Some dogs won't see
problems at this rate. Some may.
This is a much more conservative toxic level calculation than the
"standard" of 100-200mg/kg, but better safe than sorry. A dog
sneaking a couple M&M's shouldn't have a problem, but it isn't
a good habit to get into!
