On Reddit someone claimed yesterday to be blocked from Coinbase because he used the Bitcoin poker site Seals and/or Betcoin:
http://www.reddit.com/r/poker/comments/2dxuqw/be_careful_seals_users_coinbase_has_blocked_me/ Upon review of your Coinbase account, we have determined that we can no longer provide you access to Coinbase Services. Please understand that Coinbase is a regulated Money Service Business under the FinCEN division of the U.S. Treasury Department and as such, we are required to review accounts in order to ensure compliance with regulations.
Gambling is illegal under US law even if you live outside of the US we cannot provide services to your account for the purpose of any type of gambling activity.
Please note that we have not blocked access to the bitcoin balance currently in your Coinbase account; while we can no longer process transactions of this bitcoin via our banking relationship, you may send this bitcoin to a local wallet or another bitcoin address.
In the event that your controls change and you are able to prevent such activity from occurring on your platform please let us know and we’d be happy to review your compliance program and evaluate your account to see if we can support it in the future.
Seals uses unique deposit addresses and AFAIK pretty random withdrawal addresses, so I am not sure how they could recognize that.
Betcoin seems to use 1 main hot wallet according to the comments:
https://blockchain.info/address/1NyjjRGuBZ1FUSwrgizjZeHTM83RNh5uWr so that is more obvious.
So it seems Coinbase is at least tracking known hot wallets from gambling sites. Generally gambling sites will use unique random withdrawal addresses or other users' deposit addresses, but some obviously not.
If you use Coinbase and you gamble, ideally have a normal desktop or blockchain.info wallet in between and don't deposit/withdrawal immediately from/to Coinbase.edit1: Confirmation from another site than Seals or Betcoin:
http://www.reddit.com/r/Bitcoin/comments/2e2yxr/beware_coinbase_is_banning_accounts_that_play_on/In the last day we have had players who found their Coinbase account closed because they withdrew coins from SatoshiBet.com to their Coinbase account.
We heard similar stories from other gambling sites (Seals with Clubs, Betcoin, ...)
Switch to Blockchain.info folks.
If anyone has more information it would be great to hear it.
TL;DR: coinbase is blocking accounts that get withdrawals from gambling sites.