For the Like button, it's working for me. When you first post an article, if you immediately Like it, Facebook hasn't had time to scan the page to find the proper Open Graph tag, so it uses what it finds first. If you view the article, wait even like 10 minutes, and then Like it, the image should be right from the get-go. Wall posts do update automatically as FB fetches the Open Graph tags, so your wall may have even updated already.
This is the same issue. It can take time to for Facebook to scan things, depending on a lot of factors. Sometimes it's immediate, but sometimes, it goes straight to it's cache.. and if that hasn't been populated yet, you get nothing. Again, for me, if I put that link in FB, all the info properly appears now.
Hope that helps,
Alex