Also, I would suggest that you allow a larger number of lists for free accounts (more than the current five) but instead limit the number of private lists (in fact, I would argue that all lists created by free users should be public).
Also, I agree with you that free accounts should not be limited to 5 lists. In the next release this limitation will be removed. In its place collaboration features will be limited for free accounts. Forcing free accounts to make public lists is an interesting idea that I am going to consider. Thanks for the ideas!