I use the comment node and also the description tab within the node editor for documentation. It would be nice if there was something visual on the node to indicate that it had something entered into the description. Without this you cannot tell which nodes have a description, which results in only using comment nodes for this purpose. Maybe a bold border, small icon, or something in the node status area?
Also, a checkbox to show the description as a tool-tip when the user hovers the mouse over the node would be very handy.