It is absolutely ok to do this!
Here's a link to a chart showing how long human milk can be stored in various situations:
http://www.kellymom.com/bf/pumping/milkstorage.html#storage
The cool thing about this is it's stackable. This means that you can have it out on the counter for 10 hours (room temp), put it in the fridge for another 8 days, and you'd still be fine keeping it in the freezer for 6 months to a year depending on your freezer type. I actually had a freezer that wasn't a separate deep freeze but I cranked it down all the way to the coldest setting and I was able to keep milk in there for 8+ months.
You don't have to toss it at these guidelines. These aren't hard rules. Mostly guidelines. Spoiled milk is really obvious. It's got a very disctinctive and offensive odor. If it fails the sniff test after you thaw it, toss it. If it passes, it's fine to use!