DredNicolson's Quick Tips #1
Attribute nodes in Blender Cycles are normally used to pull named datablocks from an object's mesh data. It's an alternate way to pull UV layers for texturing, and the only way I know to add Vertex Color layers to Cycles Materials.
It uses a text string input field, which lets them be used in another nifty way: to add short comments directly into the node tree work area. Great for reminding yourself what certain sets of nodes are supposed to do, or storing hexcodes for specific colors for easy copying/pasting, or adding some inside-the-box documentation to Node Groups. Since they're just sitting in the work area and not connected to anything, they won't affect how the node setup works.
Unfortunately, this only works for Cycles node trees. Internal doesn't have Attribute nodes.