At the very least, it means you cannot post more than eight smileys per post. I gather images other than smileys count against this quota as well (but one linked image per post should be more than enough).
You may want to consider the "Disable smilies in this post" option if you tend to use a lot of smileys in your Posts. This way, your smileys will appear as regular "
", and you won't trigger this limit.