A couple years ago I found out the secret of how to cut an acorn squash without breaking ones arm because you're right, they're extremely hard to cut into though a seraded bread knife works the best for me.

The secret is to poke fork holes into it on one side and put it into the microwave for 2-5 minutes, use potholders to take it out, let it cool some and then it slices pretty easy. It also saves on baking time.

I found out that tip while trying to find an easy way to cut up uncooked sweet potaoes, I found out that you don't cut up a totally uncooked sweet potaoes, microwave them for a few minutes and then cut them up.