The IRS has acquiesced to the decision in Mayo v. Commissioner; this decision will be published in the January 17, 2012 issue of the Internal Revenue Bulliten according to Linda Beale. The Mayo case allows a professional gambler to deduct his business expenses in excess of his net gambling income (to create a loss).
The effects of this are minor. Had the IRS continued to fight this decision, impacted taxpayers could (and presumably would) cite this case and would eventually prevail in court.