"Free stuff" sites are never actually "free." They cost you time, not to mention make sure you've got a spam email so that your inbox isn't filled up with 600 emails by the end of the day.
These sites generally require you to fill out surveys, install software (that is normally very difficult to remove), and spend a lot of time. I used to do these sites, and I did get some pretty cool stuff out of it (a green laser pen that actually has a visible beam, still have it, pretty cool).
I simply advise that you do not install the software and / or toolbars offered. They have the highest cash value, but tend to slow down your PC to the point of freezing.
I just now realized I've had a typo in my signature for the past 3 years.