A few points and then the end of my discussion on this subject as it has been discussed 1000 times and regardless of how many times, someone lays out the real laws, people debate it.
At this time, not paying your taxes is the only way you can be arrested as a gambler unless you live in one of the few states that makes gambling a misdemeanor or Washington where they make it akin to rape.
To follow federal law, you must pay your taxes on gambling winnings.
It is legal to file as a business or partnership if you can show you were an active participant in the business (The IRS defines active participant (Read the real definition, don't ask on a forum, the IRS makes it readily available)- it is fairly broad - just about everyone posting on a forum and making bets is an active participant. Note, the IRS just found that a business does not necessarily need to have a chance to profit. It does require that you believe it could profit.) If you file as a business, you can write off losses. You can also carry losses forward into subsequent years. You can also write off expenses (Wire fees, travel, 1/2 meals while traveling for business related travel, books on the subject, payments to cappers, etc) Losses can be written off vs. other income. There was just a case in MN where a woman wrote off slot losses as a business. She played nearly every day and lost heavily. The MN courts upheld she was running a business as she thought she could profit no matter how ridiculous her notion was. (There is no law against stupidity) It seems reasonable to simply count money in as profit and money out as loss as long as you have records. I do not believe the IRS expects a list of every wager or every blackjack hand or every dice roll ever played. This would be impossible. They do expect to see bank statements showing deposits and withdrawals if they audit you.
There is no law that says it, but I believe you will trigger fewer audits by filing as an Ecommerce or Entertainment business than saying, Hey uncle sam, I am betting sports.
Read
http://www.usdoj.gov/criminal/cybercrime/kvd0698.htm for how the DOJ interprets the wire act. They very clearly state that the wire act is not to be used against mere bettors, but only against people offering lay bets at a profit (Bookies) It would be very hard for the federal government to now arrest an individual bettor after putting in print that they do not feel the wire act pertains to bettors - would seem to be a good defense to have a copy of this. I quote "Finally, I would like to comment on two aspects of existing legislative proposals regarding Internet gambling that the Department opposes. First, and most significantly, the Department strongly opposes any legislation that would seek to make the activities of mere bettors -- those not in the business of betting or wagering -- a violation of federal law" The government does not seem to make a bettor in the business by being a good bettor. The government defines in the business as a bookie. The federal government has never prosecuted a bettor. If you are lucky to be the first, well then you have some really shitty luck.
I can not seem to find it now, but I have read several times that the US government considers someone in the business of booking if they offer services to 5 or more bettors. If someone can find this, I'd appreciate it. I will look for it. I can not recall if it is an actual law definition or from case law. I believe the idea is to not criminalize saying to your golfin buddy, I'll give you 2 to 1 odds that I beat you.
-Sean