Weak signals: Lift
Whenever so come across a new service, I tend to create an account and give it a go. Unless I've got a very specific reason to persevere in the face of confusion or poor UX, I tend to abandon it - but with my account still active in case I ever want to return.
Some services just die and I receive emails from the founders of services I can barely remember announcing they're shutting down. Sometimes companies get acqui-hired by Google or Facebook or Yahoo. But sometimes I get a steady stream of notifications that users are following me on one of these services. That's when I know I need to go and take a second look.
All of this is preamble to say that it looks like I should have another look at Lift, an iPhone and web app for building better habits and 'changing your life'. This might have something to do with the recently-announced groups feature.