Since some of you are asking about it, the Beat the Feds limited time event has been put on hold.
The gist of the event was that there were a group of 4 bosses that you could fight, upon winning you received an item with decent stats.
After you beat each boss once, you got an item which offered +1% to chip drops from Vegas fights. You then completed the Bronze level of mastery and could move on to level 2 and fight each boss again.
On Level 2, each boss got more HP and was tougher, just in Mafia Wars Las Vegas. After beating the bosses a second time, your weapon that you got from the first fight got upgraded in stats.
However, this job was pulled since it was really buggy and crashing the servers. Here is the official response:
Just to clarify - this [the Feds job] has been delayed, not canceled. I do not have an official time frame for when the feds will return, but all players should be able to participate in this event in the future. I'll try to keep you updated when I get more information. Thanks for your patience!"
Will cover this event along with loot when it comes back to the game. Not likely to come back within the next few days I'd imagine.