I thought it was just illegal for a US resident to transfer money to a off shore betting site. Not to actually use it.
When the law first went into act I had to use western Union to play poker and bet online. I don't really do much of it anymore.
I am not sure about sports but I think it is the same as poker.
It is not illegal to play, put money on, etc. unless you are in the select few states that have that law in place (Iowa is not one of them).
It is technically illegal for banks to transfer money to and from gaming institutions (are we communists now or what?). However, many still do it.
You personally have nothing to worry about, unless you are rolling in massive amounts of money and don't pay your taxes on it. I have taken many payments from pokers sites over the years and haven't had any issue..... and nobody, not even the big fish who wager alot of money, has ever been charged with anything (except pry tax evasion, and you wouldn't need to worry about that unless you are really pulling in some dough gambling).
Lately though, it has been getting harder and harder to get your payouts from sites, as the DOJ apparently has nothing better to do than try to keep you from betting $20 on the Cyclones. It appears they forgot this is a free country.