Jackie,
Thx for your honest reply. We do not post the link in order to make sure that people don't just "click and try" (one of the disadvantages of web experiments is that people may just want to check out how it looks). Having lots of aborted experiment trials doesn't look good if one has to write up the results.
I assure you that your email address will not be not be given to others or used for anything but emailing you the link to the experiment (like all experiments involving people, we are monitored by the human subject board of our university [as you will see in case you decide to participate]).
Also, you don't HAVE to participate after you send us an email - nobody is monitoring that. We just prefer to know where our participants heard from us (that's why we ask you to email us first before we give you the link).
I hope that answers your questions, which I very much understand (I have similar doubts about most cases where somebody wants my email address),
Florian
