Joe Thorn has a good post up today about backsliding, how it's not something we talk about much nowadays, and what are the marks of it. Here are some of the marks (from Richard Owen Roberts) that Joe lists. Read the whole post.
3. When the biblical knowledge possessed or acquired is treated as external fact and not applied inwardly, backsliding is present.
9. When aspirations for Christlike holiness cease to be dominant in your life and thinking, backsliding is there.
15. When the slightest excuse seems sufficient to keep you from spiritual duty and opportunity, you are backslidden.
18. When there is no music in your soul and no song in your heart, the silence testifies to your backsliding.
25. When your tears are dried up and the hard, cold spiritual facts of your existence cannot unleash them, see this as an awful testimony both of the hardness of your heart and the depth of your backsliding.