Are room "Descriptions" an add-on though? For a text playing environment I'd say they were a pretty fundamental aspect! They are also something (MUD creators dependent) that can be a stable part of a MUD which for some can be grabbed and used to identify a player's position in that environment.
Notes are different I suppose, but if one is documenting a MUD (possible to share that information to others) it is sometimes that you'd want more than a short text label on the Map - besides I think it is currently not possible to edit the text that one might put onto a Map label (though if I have that wrong I can stand correction - if right, something for the future development blueprints...) - whether a data item such as "notes" is significant enough to bring into a designated item in the Room structure is what I've opened this topic to hear the discussions for and against.
I can see Chris's idea for a room properties dialogue - in a separate topic / bugtrack I've got some suggestions for the exit dialogue which I'm working on which touches on that I think. I get the idea of using part of a room properties dialogue for display/edit of all the items stored under the roomUserData - simplest would be a two column table of keys and values. I know that Filion (I'd know him as Groderick) is storing "desc" keyed room descriptions in that place and also door names using (full, unspace, all lowercased) exit words as keys, for the Wheel of Time MUD mapper (s?)he's developing.
The trade off as I see it is between adding hard-coded elements to the Room/Area structures with specific access code which may be of interest to only a small portion of users but can be optimised for their (the elements) use and the "generic" roomUserData which can be customised for a range of purposes but which each user will have to develop or source scripts to use for the way they want.