What's in your documentation?

What sort of things do you store in your documentation? For instance, do you store subnet/VLAN information? "How-to" guides for troubleshooting, the "how and why" your network is set up the way it is, etc.

What experience/knowledge level do you target for your documentation? This is mostly for how-to type documents. For instance, do you expect the readers of your documentation to understand how 802.1x works, or do you explain that in your documentation? Or do you merely link to some $Vendor documentation?

Do your coworkers actually refer to the documentation? Or... do they just ask you?