"On June 30th we will eliminate our free, advertising-supported version and convert to a subscription-based offering. As a result, you will soon be required to pay for a subscription or discontinue your service. We are eager to keep you as a member, so I hope you'll take advantage of our special Charter Subscriber pricing.
"We are doing this for several reasons. First, given the industry-wide decline in the advertising market, it is no longer possible to provide a dynamic free service based strictly on advertising. Second, we've received an overwhelmingly positive response to our subscription-based Professional Edition, and have decided to focus our resources solely on enhancing this version."
For charter members they have enabled the premium service at no charge until June 30 and are offering discounted rates. The basic rates, as low as $5/mo/person, are pretty low for the features they provide. I hope it'll keep them going!