Everything you want to know about taxes and offshore wagering:
1) No offshore book does reporting to Uncle Sam, therefore, you are on the honor system wrt offshore winnings. However, making a lot of big withdrawals which are cycled through your bank account could throw up a red flag.
2) 99% of the guys on these forums or elsewhere who gamble offshore, regardless of what they brag about or claim, are net losers over the long haul. And you are likely to fall within that category. What that means is, if you are concerned about taxes, don't be. The IRS only taxes winnings. If you are a strictly-by the book type who would like to report that 10 dollar bet he earned on the Super Bowl last year, just try to remember how many losing bets you had. Better yet, if you're that sort of stickler, keep a log of every wager you make. When the year is done, net it up and see if you won or lost. I'll bet you lost. Then if you wish to report winnings, go ahead and take the time and effort to do all the paperwork, I'm sure it will make for a fun afternoon. Then deduct your losses and owe nothing. Now, aren't you glad you did all that work?
3) Let's say you are among the 1% who actually wins long haul. You then can be subcategorized again: 1) a guy who follows the law wrt taxes and pays what he owes. 2) the 9,999th guy who comes to this forum and wants to know how to evade his taxes. While I'm all for "sticking one to the man", in the case of the IRS I'm firmly against it. This is a bureacracy that knows no limits when it comes to screwing you over if they set you in their sights. It is better to err on the side of caution than to play silly games with these guys. It's a choice between being worried all the time that your shenanigans will be exposed some day, versus simply paying what you owe (better yet hiring a good tax guy to handle it for you) and having peace of mind and enjoying those offshore winnings. Gamblers are under scrutiny in the first place, so don't multiply your worries by pretending you're Al Capone; you're not. Taxes suck but being audited and fined (or worse, federal prison) suck more, and that's the bottom line, imho.