System or freeform...I dunno either...
As always, I would prefer to not do freeform, but we can't do a by the book battle in Battletech turn by turn either. We'd be running one small fight for the better part of a year in a play-by-post game. Ick.
I think the way we were going to do it in the game Robguy started all that time ago was a nice little hybrid idea. Wish I could remember the specifics, but it was basically initiative rolls to determine early advantage, freeform style writing keeping that roll in mind for the 'slant', then based on peoples posts the GM might make some behind the scenes 'rolls' to see if actions that could potentially turn the battle succeeded or failed and add an element of chance into the outcome of a battle. Sort of like refreshing that original initiative roll, actually.
Players would rarely, if ever, actually have to handle the dice. Going with good posting ettiquette, meaning that players never determine themselves if one of their attacks hits or actions succeeds (except for the trivial and mundane to which there's no reason the players can sort themselves out), the GM can make the occassional, important, hidden roll and just post the results of the player's action. Most of the time the GM wouldn't need to, unless they felt inclined to, mind you.
Robguy, wasn't it something like that? Care to elaborate?