Is there a way to make comments in the node editor? I'd like to have a node like the Frame node but one that can have lots of text, not just a header. I've looked and it looks like there isn't any such capability so far, so I was wondering how easy it would be for someone to create a custom Comment node as an add-on or script (I don't know the differences between the two). I myself would love to leave detailed comments in complex node trees so that I can figure out what I was doing/what to do when I come back to them months later.
Since version 2.74, blender has has the ability to display text blocks in the node editor.See the manual.

Add a frame node, then in the properties region add the text block you want to display. (A text block is simply a file made in blender's text editor.)

The frame will display the text exactly as it is in the text editor without word wrapping, you have to add the line brakes in manually (by pressing Enter at the end of the line).
This is the easiest way to make notations in the node editor.