When it comes to make a purchase decision, less available plans will get higher conversions from indecisive customers. GetMarker knows about it and other samples can include OpBeat former pricing page.
ActiveCampaign does not ask for entering your password when creating an account within their site. Once you have enter the initial fields (email + company), a modal is automatically triggered to ask for setting up your password.
Another great example of how UX can hack your signups.
Unroll.me limits its usage to 5 un-suscriptions if you don't share the tool with others.
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.
Quibb, and other sites like ProductHunt.com or DameCaoba app, know the importance of playing with exclusivity and limited-access in order to generate buzz and interest. Hello ProductHunters! :D
After signing up in Twitter you have to walk into the tour/demo no matter if you want to go other section, you can't.