Hi Sarah,
Do note that the 'use first image as post cover' setting is only for the listing page, not the entry page.
If you do not want to display the post cover in the entry page, you need to disable the setting in Settings>Views>Entry Layout>Show Post Image(http://take.ms/eCIqg).

when it posted to facebook, there was no image showing.. just an empty placeholder

I tried your post entry page in FB's debugger and it seems to crawl the image properly(http://take.ms/sgm6I). Am I missing something here?

Sorry. I am probably using the wrong terminology. If you go to our blog link, that first page it takes you to, you will see for our latest blog that it is showing two images there (the post cover and another image from that page). Why is it showing the second image? With facebook. When we removed the first image and made it the post cover, when those changes autoposted to FB, that is when you saw the placeholder, no image. I deleted it from FB. I might have to wait until we do another blog so I can replicate the issue in FB. Should the post cover appear in the FB post?

Hey Sarah,
I see. So you are referring to the listing layout. The first image is the post cover and the second image is the truncated content based on what you set in the truncation setting. The other 2 posts also contain images from the truncated content.
The difference between the first post and the rest is that the first post contains a post cover plus the image from truncated content, that is why you are seeing 2 images.
If you do not want to display post cover in the frontpage, you can disable it in the frontpage view setting(http://take.ms/kB62N).

For the Facebook issue, I have tried to replicate it locally but it is showing the post cover/first image properly. To answer your question, the post cover should appear in the FB post, and if there's no post cover, it should get the first image.