I just read this article and thought it was good to share.
This just seemed like a given to me but apparently a lot of people don't know that when a container says "microwave safe" it really has nothing to do with whether or not the plastic will leach BPA, but that the container won't melt in the microwave. BPA is a dangerous chemical that companies in the US are only now starting to warn consumers about despite the fact that plastics that leach BPA are being banned in many countries. You should NEVER microwave plastics that leach BPA, or freeze them either for that matter. Extremes in temperatures cause the plastic to degrade which leachs BPA faster into the food or liquid.
What other options do we have then? Well, there is always glass or ceramic, which may be more expensive, but it will last you longer (pending breakage), heat more evenly and is better for the environment. Another plus that I have found is that with glass, food can be baked, served and then stored, all without changing the container. Less dishes to wash! Yay! One mom suggested looking at thrift stores for old Pyrex which would definitely save a lot.
What plastics should you look out for? You should definitely avoid: #3 PVC, #6 PS, and #7 PC. The "safer" plastics are coded as such: #2HDPE, #4LDPE, #5PP and PLA.