I put my own photo as my profile picture because it's my profile? I think people have a right to see who is posting etc. But yeah...there are the totally vomit worthy ones (people taking their own picture in the reflection of glass comes to mind).

As for those with kid or group photos...i think it just suggests they have a healthy interest in what's important in their lives, though to be honest i don't find it that useful in terms of identifying people etc.

Generic ones seem to me to be either a lack of confidence or a concern with privacy.

Just my thoughts anyhow...