Given what has been said about how epic combat in Elemental will get, I think it would be nice for players to be able to share their best battles with eachother.  At the end of each battle there should be an option to save a replay of it.  The replay should then be viewable from a 'View Replays' option on the main menu.

To keep replays valid between different versions of the game there are two options.  The first is store all data for older versions of Elemental and have the replay include the version number and actions taken(this would have Elemental reconstruct the battle like RTS games).  The second, which I like, is for the replays to include data of the results of actions with actions taken(instead of having Elemental simulate the battle like RTS replays).  The first would make replays smaller than the second, which has the advantage of not having to store data for all versions of Elemental(Given the way Stardock updates its games there will be a lot of different versions).

Ideally, replays should be stored in two different folders, one for the player's replays and one for downloaded ones.

What would be really nice is if Stardock could use Impulse to manage downloading replays or, even better, integrate downloading them right into Elemental.