I read today that online gambling revenues are about $12 billion.
The entire US economy in 2005 was $12.4 trillion (CIA factbook).
If every dollar of online revenue came from the US, $12 billion in $12 Trillion is $1 of of every $1000 in the econonmy.
Since only 50-70% of the revs are from US, say only $1 of every $1800 in the US economy is spent gambling online.
Hardly a big deal for the economy, but bad enough for addicts.
In contrast, Anheuser-Busch sells $15 billion in beer each year. Our whole industry outsold by 1 company. 
That is, well…..a sobering thought.