My understanding with Zynga speculators is that the US may soon legalize online gambling and that Zynga is well-positioned to take advantage if that happens.
The reasoning is two fold, first gambling is considered a 'sin' by many religions (which is why Las Vegas was sometimes called 'sin city') as was same sex marriage. There is a chance we will finally clear the way for same sex marriage after a decade of staunch resistance by religious interests, and if they 'lose' that fight they will certainly try to draw a line in the sand with gambling. These same interests have been trying over turn the right to privacy ruling which made abortion legal.
EDIT: add reasoning.
The issue with online gambling is that in its previous form, when it was finally and fully outlawed in 2006, the Federal and state governments weren't getting their cut of the take and many people weren't reporting winnings to the IRS.
Its not especially a moral or religious issue now, its more a taxation and revenue issue. The House Financial Services Committee approved a bill to legalize online poker and some other forms of online gambling in 2009, it just hasn't made it all the way through Congress yet. I imagine there will be some Republicans opposed to it on religious grounds but once Congress figures out how to tax and regulate it and how much revenue they can rake in off it, it will be back.
Keno and other forms of gambling are legal only in Atlantic City and Nevada, for historical reasons. Gambling is not illegal in reservations but "indian" casinos are generally subject to approval by the federal government.
Congress has known for decades how to tax gambling revenues. They have simply chosen not to do so. Generally, the justification for not legalizing gambling nationwide is that the tax revenues raised from gambling activities is far outweighed by the increase in crime and decrease in properties values.
Congress chose to outlaw online gambling in 2006 as a result of many, many individuals developing chronic gambling addictions that destroyed their own lives and the lives of their families. The alternative was heavy regulation, but the casino industries (Vegas, Atlantic City, and various tribes) fought against it.
Gambling is legal throughout the country to varying degrees in various forms. Black Hawk, Colorado has legalized gambling up to $100 per bet, for example.
If gambling is going on in Black Hawk, CO, it is not "gambling" within the legal definition of the term or it is not legal. Alternatively, it may simply be an office for a (legal) sports-book operation that operates out of Nevada. Chances are, however, that it is not a legal operation and simply does not do enough business to warrant federal resources.
This is why there are no casinos (other than indian casinos) outside of Nevada, Atlantic City, and reservations. Do you really think that California wouldn't have a billion casinos (in addition to the Indian Casinos) if they weren't prohibited from doing so by federal law?
Gambling generally means any wager for cash, where skill does not play a role in the chance of winning the prize. Skill generally applies to intermediate steps en route to winning, not "skill" in selecting the prize-winning item. This includes lotteries and horse racing, but these forms of gambling are specifically excepted from the gambling prohibition. Most traditional casino card games are considered games of "skill" rather than gambling, which is why card houses are legal (subject to local restrictions).
Sports books are legal, so long as they are based in a state where gambling was legal when the gambling prohibition took affect.
The Mississippi gulf coast has had casino gambling since the 1990's when it was authorized by the state, http://www.worldcasinodirectory.com/mississippi.
Colorado voters legalized casino gambling in BlackHawk in the 1990's as well, http://www.blackhawkcolorado.com.
Detroit legalized gambling in the 1990's, and a number of state legalized it on riverboats on the Mississipi in the 90's as well.
The Federal laws on the subjects mostly apply to interstate gambling enterprises which is where they do have jurisdiction, in particular sports betting and the 2006 law which outlawed online gambling primarily by preventing banks from transferring funds to and from online gambling sites.
One step at a time. And only a matter of time before the 72 hour lottery pool morphs into millisecond real time gambling.