It's not social at all at the minute. Sharing folders between users is an idea we've been discussing, but nothing's come of it yet.

We email users every time there is a large update to the site with a fairly high open rate. However, not many of them return to give us another go.

Would it make sense to send a reminder to users stating something to the effect of "you have 200 new tweets that need to categorized?"

We could do that. As a user, would you personally find that useful or would you class it as spam?

Try it one week and see how many people unsubscribe. Our team is also very critical of email notifications so we try to think like normal users. As long as you make the email insightful or interesting, users wont mind.

A great v2.0 feature would be to use NLP and automatically tag and filter the user's tweets. It would be hard feature to pull off but it would take your product to the next level.

Can you kill the landing page? Maybe users would like to browse other user's folders and discover now content.