You should (I think) adjust the amount of karma received for reviewing negative thoughts downwards. In my experience people are the type of animal that likes to sniff others' poo and will gladly offer opinions on them even with a smaller reward :-(
The invite-a-friend form is broken on Firefox 3.6.8. I only get a text field with an URL in it by default (http://www.endants.com/?r=42), and no way to submit the form even after I enter an e-mail.
Your feedback on both these points is noted. I'll fix both of them. Thank you!