In perusing my referrer logs this afternoon for the first time in some months, I was annoyed to see that perhaps 90% of the entries had something to do with (you guessed it) poker.

In doing a little digging via WHOIS, I discovered that all but two of the twenty-odd different recurring poker-related domains resolved to the same IP address: 64.4.195.62. So, you might just want to add this address to your IP denial list -- not sure if this will keep the associated links from stinking up your referrer logs, but it can't hurt.