Laura, check out the Guidelines for Milk Storage from the Human Milk Banking
Assn, and the articles in the JHL on milk storage. Since human milk (I prefer
HM for human milk to bm for breastmilk) has living, active cells, it's less
perishable than other fresh foods. Refrigeration is always preferable. Barger
and Bull documented that freshly-expressed milk showed no rise in bacteria
levels in clean containers left at room temperature 6-10 hours. This doesn't
mean that moms should leave milk hanging around the house, but it does mean
that one needn't panic if refrigeration is a bit delayed.  Refrigerated milk
is safe for up to 5 days, but develops an off-taste as it ages. Once frozen,
the white cells are killed and it should be treated like other perishables.
Pretty good stuff.
Linda Smith, used frozen milk on a burn with great results.