No apology necessary, I'm at work, ill. Bronchitis. Totally understand.

I don't know what you mean by mothballware. Care to elaborate?

I don't think there's a risk of seeming like you're cutting people off. So long as you're up-front with people when they sign up then there's no problem with this. The value is in the ability to add and edit your bookmarks. Being able to access them later is trivial if you're looking at it from Tinmark's perspective and from a user's perspective this is the same as getting a try-before-you-buy premium account.