No boring introductions, just take a look:
There is another hack related already included in petithacks. We can see how they are pushing the referrals (now with a discount in return) to grow faster.
If you want to see it live, sign out of your Mailchimp account or go directly to their http://mailchimp.com/see-ya-later/ url where you are redirected after your sign out.
Other similar companies doing something like this are KISSmetrics - also in the logout screen - and Intercom - in their signin screen. I will add them in a few days!
Less action required from the user (no need of clicking anything else, or entering an email), more probability of having them back to their tool.
By having a biz model not based in a 'pay per month', but triggering adverts within the app, for Unroll.me it's essential to have more and more users. Something that they are achieving with tricks like these one.
All for the sake of activating sleeping users!
Another great example of how UX can hack your signups.
Don't know if this can be considered as a 'hack', but they created another service on top of their classical pay-per-minute, to get more revenue from their users: a subscription model to attend private online talks given by hand-picked pros.