And in the end, when I want to sell WoW weapons, buy webserver space, or play a few games of poker online, why would I use gold, credit card or paypal, which all require me to remember log-in creditials, give away information and/or pay a bunch of third party fees.
In the United States banks were ordered to block these transactions under the Unlawful Internet Gambling Enforcement Act of 2006 ( http://en.wikipedia.org/wiki/Unlawful_Internet_Gambling_Enforcement_Act_of_2006 ), though there are some poker sites that continue to accept US players following Black Friday.
For BitCoin poker SealsWithClubs.eu (available in the US) runs exclusively on BTC deposits and withdrawals while SwitchPoker (US players not accepted) takes it as a deposit method and then converts it to fiat. Another site, InfinityPoker, which has been in beta for close to 6 months plans to also be available to US players and will accept BTC as a deposit method and convert it to fiat (and back to BTC when you withdraw).