This is my major concern from the beginning. Not all users erase their cookies frequently. But some do.
Don't count on it, with free software, managing cookies is easy for everyone. Folks are aware of cookies and are deleting them. http://www.ampsoft.net/ Download the free "cookie monster" software and you will see what I mean. This is some great software.
I am an overseas affiliate and have serious problem with Linkshare. I have been playing the game for 2yrs., I got no commission no sales but lot of clicks, I found that on the merchant payment history I did receive payment from all merchant that I joined at least in the pass 6mths., but I got no commission, I email Linkshare but they didn't reply, I also email the merhant but also the same, they should at least tell me the reason, there must be something wrong with them, so I disabled my a/c and out of the game.