Here's something else I'd like to see. The great thing about this idea, by the way, is that it's largely cosmetic and so (hopefully) it wold be relatively easy to code in at this late stage.
Now, take a look at
this se5 screenshot from malfador.com.
See where it says "surface", "races"...."Abilities"? I'd like to see an additional tab there, called "notes". When you click on this tab the game would search for an external text file named after the planet, in a folder named after the game, which in turn would be kept in a special "notes" folder.
By default, this notes/gamename folder would be empty. The game doesn't generate anything at all to go in there, so it isn't taking up any extra disk space unless the player chooses to create files himself using notepad. Also, the file would only be stored locally, and would be for the exclusive use of this player, so these notes would be completely secure and wouldn't bulk out the savegame files at all. This also means that each player could keep their own notes about each planet- you could annotate your own planets, enemy planets or any other planet as far as you liked, without interfering with or seeing notes made by other players. Of course, players would be free to email notes files to one another and trade them or merge them or whatever, but that's all happening outside of the game mechanics so we don't need to worry about it.
Ok, so you've clicked on the "notes" tab. If no notes file for that planet is found (which is the default, remember), then nothing is displayed. However, if the file is found, what happens next is pretty obvious. The contents of the text file are dumped into the window. Players could keep game information in there ("atmosphere conversion due to complete in 2422.8", "Had 3 CSM weapons platforms when I attacked it on 2416.4") or roleplay information ("this is where the 3rd fleet gloriously brought the Phong Empire to its knees", "This is where the enemy's third fleet notoriously brought our empire to its knees") or absolutely anything else you like ("mum's birthday next week, buy flowers").
The file could be plain text - that would be fine - but some markup would be even nicer: a few select html commands would go a long way and would allow roleplaying players to publish their notes direct to the web if they wanted. H1, H2 tags etc spring to mind, UL, OL and the like. Tables might be overdoing it a little, but IMG tags would be cool. Imagine if you could use href tags to set up your own links and click the game directly from one planet to another- very handy for executing population tranfers etc.
Finally, this system needn't apply only to planets- it could be done for asteroids ("Claimed by Jraenar under treaty of 2413.1"), stars ("going nova on 2406.3"), and ships and fleets too ("commissioned in 2402.2, destroyed three enemy light cruisers in battle of Ceres").
Imagine the possibilities...