By far the worst Fog of War I have ever seen was in the first Mechcommander game. The developers used a limited color palette as an excuse to only have one layer of fog. All black or totally revealed. And once you revealed a location you had line of sight to it for the rest of the game.  It was very easy to suicide a light scout Mech into the enemy base right from the start and, even after the Mech had been destroyed, see every move the enemy team made because that spot had been cleared for the rest of the game.  What was worse is you also had access to off-board artillery so once you cleared the fog with that initial light Mech you could proceed to attack the other team's units and structures without ever risking any of your own units.

I really liked the concept of that style of multiplayer though. It was the first RTS I had seen where you didn't construct your units in the game. You built your team before the game started and once they were eliminated they were gone for good.  It was an awesome idea with tons of potential, however ultimately ruined with something as silly as incorrectly implemented Fog of War.

Most RTS games give you a choice. SupCom  gives you the option of no Fog of War, Explored (where is starts out grey-ish but you can see all terrain)  or unexplored (where everything starts out totally black). That's great, everyone has their own preferred style and they can set up the game how they want. But if they force everyone into only one type then I think it really limits the audience and it won't be as popular. So hopefully they will give SC2 the option and not just lock them into a single form. Blizzard tends to be very good at what they do so I don't think they are going to screw it up. ;)