Family Properties and Lost Mafia Strength

Have you noticed sizeable reductions in their Mafia Attack & Defense strength? The Mafia Wars team made an explanation this.  Here it is:

1) Because any items you add to your Family Properties are removed from your personal inventory, their Attack & Defense strength is no longer applied to you personally, but to your Family Property instead (so choose those items carefully).

2) Building the first Family Property, the Artillery Station, grants you a Family Property Bonus of 1,000 Mafia Attack Points, but only when its health is at 100%. The Family Property Bonus you receive is reduced when the property is damaged as the result of rival families robbing from it, so you'll want to repair it to keep its health (and the Family Property Bonus) at 100%. Also, 1,000 Mafia Attack Points is just the bonus for a Level 1 Artillery Station; you can increase the maximum possible Family Property Bonus awarded by each property by upgrading them to higher levels.

The Mafia Wars team hopes this explains what the recent shifts in your Mafia Attack & Defense strength. In reality, the biggest changes are likely from a rival-family robbing your Artillery Station and reducing your family bonus.