A new feature was added in Mafia Wars today called "Declare War". Here's a picture (click to enlarge):
Yeah, I whited out names and pictures for privacy sake.
But anyway, so far it looks pretty cool. Basically you can "Declare War" once every 12 hours on your friends! When you see the portrait, you can click attack on them.
If you win the fight, you get a couple XP (not sure if you get any items yet) and they just "die". They do not take any damage and it does not cost any stamina, which is nice.
If you lose the fight, you wound the enemy and it still seems like you get a couple experience points. It seems that 2 woundings kill someone, regardless of the strengths of the attackers & defenders.
Needs more rewards. I won a war of my own, got nothing, and I ended a friends war by killing the last person, got nothing. No EXP bonus for winning a war, just the 3 exp or so for attacking someone.
If you share Top Mafia with someone, it does not work out too well. I do not think the developers thought that one through; hopefully they come up with a work-around for that one.
Some people do not like the ideas of attacking their friends. I think it is great, it makes the game much more interactive. Honestly it is a lot more fun to me attacking a real life friend then it is attacking Joe Blow off the fight list or hit list for the 1932482th time in a row. I think these people will change their tune if the developers attach item rewards to war.