Automatic "Mark Posts Read"

Not sure if anyone has thought of it before as a possible feature, but how about an option that automatically marks posts read everytime you leave the site and/or log out?

I could, but a couple of years ago we had a discussion where people decided they didn't want that. I tend to agree. There are other forums I visit where it's automatic, and as such I feel like I have to read everything or miss something when I come back because I don't remember what I did or didn't read.