Nice to see that you have started on a thread from 2003 
When it comes to conversion for us it is so much that could change that number, we have affiliates with an amazing 58% conversion from signup to deposit down to under 10% for others.
For us it depends from which country the players come from and also what products they are promoting and how they promote. Some forums manage to get a very high conversion, and those that have general forums and send out newsletter to them might get a lot of signups but few depositing clients.
I want to see a signup to deposit % on roughly 20+ % to be ok with it. If it is less we try to increase it, and if an affiliate has higher we try to see what they do to get those numbers.
What is important is the click to signupratio as well, cause if they click on a link to our Casino and then dont sign up, you always wonder what can we do better to actually get them to finish that important step to signup but it is a continuing experimentation to get that perfect.
Cheers
H