Is it bad to boil milk?
Significant loss of nutrients during pasteurization is simply a myth.

According to the National Council Against Health Fraud, the loss of nutrients when pasteurizing milk is very small.  Most nutrients are unaffected.  There is approximately a 10-20% loss of vitamin C, 10% loss of thiamin, and 0-10% loss of vitamin B12.

See the linked article to get their detailed references.

They also mention:


  The Family Cow
  
  People who remember "the good old days" when many Americans had a
  family cow, often ask why they did not get sick from drinking raw
  milk. The answer seems to lie in the fact that people exposed to the
  same cow, or cows, on a regular basis develop a conferred immunity to
  the microflora of their specific animals. It is when raw milk is
  marketed to the general public who has not been regularly exposed to a
  specific animal, or small number of animals, that infections occur.
  Further, the people primarily at risk for serious infections or death
  are those with undeveloped immune systems, such as babies, or adults
  with disorders that have compromised their immune systems. Healthy
  young people and adults who are infected are likely to believe that
  they have had a bout of "stomach flu."


While boiling milk at home may be somewhat different in its actual outcome, I would suggest that the health benefits of mitigating the risk of food borne illness vastly and completely out weigh any potential loss of nutrients.