Along with the addition of robbing, there is now a mastery system that allows players to "level up" as they complete more successful robberies.
There are 10 total levels, and each level confers a new title to the player along with a "reward" of some sort. Here is what is known so
Level: Title earned for mastering level, # of heists needed, bonus earned for making it to the next level
[For finish level 1 and reaching] Level 2: Burglar, 10 heists, 6% bonus XP for robbing
Level 3: Master Burglar, 25 heists (more heists, the 10 from the previous level do not count), 7% bonus XP for robbing
Level 4: Apprentice Robber, 100 heists, 8% bonus XP for robbing
Level 5: Robber, 500 heists, 9% bonus XP for robbing
Level 6: Master Robber, 1000 heists, 10% bonus XP for robbing
Level 7: Apprentice Thief, 2500 heists, 12% bonus XP for robbing
Level 8: Thief, 5000 heists, 15% XP for robbing
Level 9: Master Thief, ??? (guessing 10,000) heists, guessing the bonus will be ~20% XP bonus
Level 10: Grand Master Thief, ??? (guessing 20,000) heists - this is the title for level 10 - I am not sure yet if this title will be granted to the player simply for reaching level 10 or if the player has to max out level 10 mastery first. I'm guessing the reward will be ~25% XP bonus, along with an item of some sort. It has been stated that we will receive an item reward, just not sure what it is yet. It will be awhile simply due to the large number of heists needed to get this high, but perhaps we will find out early if someone exploits!
Note that quality of type of heist does not matter for leveling up. The only thing that is important is winning. You do not get bonus mastery % for robbing high-stamina cost targets (Casinos etc). As a result, you want to focus on robbing low stamina cost targets.
If your board looks like this:
Flophouse x2 (costs 2 stamina to rob)
Pawn Shop x3 (costs 3 stamina to rob)
Restaurant x2 (costs 7 stamina to rob)
Mega Casino x2 (costs 20 stamina to rob)
..by robbing (successfully) the 2 flophouses, you will add 2 successful heists to your total, while only spending 4 stamina (10 times more efficient than robbing casinos).
As a result, I recommend never robbing casinos (unless you are trying to collect cash or XP). It's simply a lot faster to level up your robbing mastery by robbing everything but the most expensive targets (casinos, uptown hotels, and even office parks) and getting new, cheaper targets.
Think about it this way - you can leave 4 properties unrobbed each time and for only a 4 stamina cost, however, simply by robbing a Casino over a Flophouse, you have spent 18 more stamina!
In short, rob the cheapest properties and then refresh your property page.
In other news, I'm not sure if we will see an Easter event or not. It's in between being a Christian holiday only and being secularized, so I wouldn't be surprised if there is not an event associated with it. Holiday events didn't become the "norm" until the 4th of July event, so there's no way to know for sure since we didn't see what they did last year.
Also there's a few new free gift items, so if you're into collecting weak loot, it's your lucky day!
You can also get a new 51 attack, 30 defense weapon (Pocket Rockets) by leveling up in Zynga Poker. The reward system is buggy as usual, can't help you there if you didn't get it! The only tip I have for you is to go into your achievements page in Mafia Wars after you have earned your levels.