I am currently working on a project that is a series of websites that each offer a free service (one is file hosting, one is user uploaded videos, one is user uploaded pictures, etc.). I am planning on having the user accounts shared across all the sites so they do not have to register multiple times. The part where CPA comes in is that I will offer incentives for users to upgrade their accounts, earning additional benefits for each site(unlimited files, higher file size limit, etc.). What I am having trouble planning is how to balance these benefits. I was originally thinking doing an offer would upgrade an account for life, but maybe it would be better to have it for a certain amount of time to have offers completed multiple times. This, however, would make less people to complete the offers because the incentive is not as great. This is what I mean by balancing, generally how good should I make the benefits against the amount of money I will make? I haven't gotten any sleep and I feel like I am rambling on and I don't know if you even understand what I am asking. Long story short: is it better to have a lot of crappy incentives (less chance of being completed) or a few good ones (more chance of being completed)?