1. If appropriate, deep integration with facebook, twitter, linkedin etc, not only to ease registration process but also for sharing content(in both directions)and other social features.
2. Utilize FB API to provide a social network around your service and let users share/comment/discuss/rate/etc. about your public things.Provide top rated/discussed thinkeries somewhere on your home page.
3. Instead of making it just public and private, provide access levels - public, friends, private, customized, etc.
4. Mobile application for quick/anytime/anywhere thinkering.
5. A search interface for searching public thinkeries and adding them to your own collection.
6. Facility to add thinkeries through SMS, email, chat etc. example - SMS your new design/startup idea to your thinkery using short code or forward an intersting e-mail to your thinkery. That leads to another idea that e-mail and chats can also be a kind of thinkery items.