The asynchronous follow model is starting to catch on. If you are interested, you follow. If you are uninterested, you leave. That is it. The internet works this way and many other services can capitalize on the simplicity of this type of UX.
To me, Twitter has become the entire internet wrapped into a neat little package on my iPhone. Like the internet at large, Twitter is a content generation site where I consume news, blogs, and thoughts from the people and organizations I admire. Everything I need is there for me. I just open it up and read.
Eventually, I see this applying to every part of my life.
In a world of pure efficiency, every service I need will be available on my time, tailored to me.
If I want to learn Japanese, I "follow" a language program where I interface with the app for 1.5 hours - 4 times/week until I stop ("unfollow").
If I want to visit Rio de Janeiro this summer, I "follow" a payment program where I approve to pay $200/month for 7 months, I can pick and choose activities and sites for the trip in the meantime or cancel, "unfollow", the program at any time with no cost.
If I want to socialize tonight, I "follow" the people and organizations I care about and choose from the various meetups, dinner specials, parties, and entertainment planned for 7pm -11pm tonight.
Each are just one example of the broad applications of the education, time management, and social spaces, respectively.
The asynchronous follow model provides for a simple, flexible, and user-centric experience. And if the application is compelling enough to get off the ground, the system can gather data to provide an exponentially better UX over time.
Apps like these will make my life better, so they are probably worth building.