When do you read Facebook Posts / Twitter Tweets?

Depends - are you referring to engagement with your personal or professional accounts/contacts?

Personally, with my friends on those sites I will engage with them when I relate to something they post. It's funny, or I've been there, or it was interesting, or epic.

Professionally, with companies or brands I friend, I only interact if A) I have an issue I want resolved or want to comment in a highly positive/negative fashion, or B) they ask a question or take a poll of their consumers. Every now and then I will "like" something on a brand's page as well.

I find that Twitter is really hard to have "conversations" - I mostly just glance at Tweets and move on.
Facebook is MUCH more conductive to the back-and-forth type of engagement.

Disclaimer: I tweet for my company.

My wife and I are both transplants with friends and family around the world.

I like quick notes and updates on people lives with an occasional pic.

X2  Good explanation!

Most of my tweets are with my lax (lacrosse) guys, companies, pro's etc, and we either have short convo's about our day, camps, equipment, funny elements, or just to say to get in touch.  I will usually also use it because I write many articles and am well known to reach out to ensure the community spreads the word, and they will all send me feedback, short tweets about what they thought, or just to tell me to call them.

Facebook I am much more social and will converse more because I don't have as much of a limit in words.  Therefore, the message can be more personal, and it's usually friends and family, and it's usually funny comments, meaningful stuff, and just elements that catch my eye that are worth me commenting on. 

Facebook I mostly comment on family events and things going on.  I don't use it a ton, but two or three times a week.

I love technology and social media, but I can't for the life of me understand Twitter.  I've signed up and forced myself to use it 4 or 5 times and it just makes no sense to me whatsoever.  It's so confusing to follow anything on there to the point that I just don't use it at all.  (sorry, you hit my twitter nerve) <rant off>