OK, one more suggestion and I’ll cool it
Have you ever considered white-labeling the sign-in for visitors of users’ sites? What I mean is that people visiting my site might not know what List.ly is. When they click to comment on a list item there is a window that asks them to sign into List.ly. I’m wondering if a premium user could have the option of having that window say, assuming my site was called “XYZ Blog”, Sign in to XYZ Blog. Of course I would understand if you didn’t do this because it limits exposure to your brand but it would create a higher level of comfort for the visitors of your clients’ websites and blogs.