I always used to think that group initiative, especially d6 group initiative, was both incredibly boring and unrealistic. I have used d20 individual initiative, plus Dexterity modifier, in my Mutant Future campaign, and I have been generally happy with that.
Recently, in my friend Carter's Labyrinth Lord campaign, we switched back to by the book group initiative. The key thing that I had always failed to grasp when I read the initiative rules was that initiative was rerolled every round. This is a ton of rolling if you are doing individual initiative, but really not hard at all if you are doing group initiative.
Short story: I really like d6 group initiative, rolled each round of combat, ties meaning simultaneous action. It allows the tide of battle to change rapidly, it allows dramatic things like knowing you are already dead but getting one last attack in (and the chance for the ultimate cinematic moment, the simultaneous death shot), and it actually takes less time than the mess of going around the table and recording initiative rolls and constantly having to remind everyone when it is their turn in the initiative order.
I think I am going to switch my Mutant Future game over to this system, and I am seriously thinking about switching my 4e game over as well. I have to think about that latter proposal a little more, as there are feats that you can take in 4e that improve initiative (I am not sure if any of my players have taken these feats, but if they have, it would be cheesy to completely castrate their usefulness). I still think I am going to do it, and may just allow players to pick new feats and or powers if they want to given this new information.
I really like the way that this simple change in initiative has made the combats in our Labyrinth Lord game WAY more exciting, and I see no reason why it wouldn't work in other systems as well.