I suspect that you will get a wide range of answers to this question, and it will boil down to how your site is positioned and what marketing tactics you are pursuing as to how you are converting. For example, a generic unique visitor is going to convert differently from a pre-qualified unique visitor. This could be due to where your links are placed, what search terms you are optimizing for, etc. Rank high for “online poker rooms” and your conversions will be better than ranking high for “poker freeroll tournaments”.
That said, I’ve been going by the rule of thumb that 1 unique visitor = $1 in revenue. Our stats seem to track fairly close to that.