The House Financial Services Committee approved the Internet Gambling Regulation Bill (H.R. 2267), 41-22, a first step towared legalizing, regulating, and taxing online gambling. Horse racing is protected under the Interstate Horse Racing Act, so whether this bill passes or not has no impact the legality of ADWs. If it does, however, it could mean new regulations and taxes on horseplayers. 

HR 4976 is the tax bill that has to come out of Ways and Means before anything else moves forward

H.R. 4976:
Internet Gambling Regulation and Tax Enforcement Act of 2010

3/25/2010--Introduced.
Internet Gambling Regulation and Tax Enforcement Act of 2010 - Amends the Internal Revenue Code to: (1) impose an Internet gambling license fee on Internet gambling operators and an additional tax on unauthorized bets or wagers; (2) require such operators to keep daily records of gambling deposits and file informational returns identifying themselves and the individuals placing bets or wagers with them; (3) require operators to pay state and Indian tribal governments a 6% fee on gambling deposits; (4) require withholding of tax on net Internet gambling winnings and on the gross amount of winnings of nonresident aliens; and (5) extend the excise tax on wagers to include wagers placed with the United States or any commonwealth, territory, or possession by a U.S. citizen or resident. Directs the Secretary of the Treasury to make grants to states to carry out an American Heritage Program through state arts agencies. Allocates .5% of the tax revenues attributable to Internet gambling to the American Heritage Block Grant Fund to finance the American Heritage Program. Amends the Social Security Act to establish the Transitional Assistance Trust Fund to finance state plans for transitional education and job training assistance to individuals who are, or were formerly, in foster care. Allocates 25% of the tax revenues attributable to Internet gambling to the Trust Fund. 

I have no idea if any of this would apply to ADWs but a 6% tax on deposits would suck.