I am in the same boat with you (kcalw) and in my case (probably yours too), it is because we answer honestly about our ages, income, family size, etc.
I am reticent (but will do so if it becomes necessary) to just lie and make up attributes that WOULD qualify me to complete these credit sourcing surveys. The number of times that they have stiffed us alone would justify that!
But the free credit sources that require only that you view their ads have increased such that almost weekly (or sooner) if you can visit these every day, you can gain 75 credits by cashing in 50 views. Also now, there are pop-up views for straight credits now, almost daily!
But all these ads DO install themselves into your computer (unless you have a resident "stop allowing ads" program activated).
http://download.cnet.com/Spybot-Search-Destroy/3000-8022_4-10122137.html
This spybot removal program will bag all of them!