I don't think this is a threat to buffer. There are two components to the buffer business:
1) the software: this can be copied or re-implemented fairly easily (see this new project). Happens all the time. Almost every product has an open source clone.
2) the schlep: doing marketing, building a business, keep the servers humming, pay the bills, be available and respond to customers...
The second part cannot be copied easily and takes a lot more effort and commitment than the first. This is what makes a business defensible and viable. And this is what separates companies like Github, Heroku, etc. from "Look-what-I-built-over-the-weekend" projects.
There's also the Buffer ecosystem; they have an iPhone app and they're already built-in as a sharing feature on many iOS & Android apps. It will take a while for Circular to match that. The more I look at what Buffer is doing, the more impressed I am.
1) the software: this can be copied or re-implemented fairly easily (see this new project). Happens all the time. Almost every product has an open source clone.
2) the schlep: doing marketing, building a business, keep the servers humming, pay the bills, be available and respond to customers...
The second part cannot be copied easily and takes a lot more effort and commitment than the first. This is what makes a business defensible and viable. And this is what separates companies like Github, Heroku, etc. from "Look-what-I-built-over-the-weekend" projects.