WordPress.com has introduced a new API today called WordPress.com Connect. It's an API to allow websites and applications to offer login capability for WordPress.com users.
It's not surprising Automattic has introduced this feature. After all, they have tons of services that obviously already use something similar to link their WordPress.com, Akismet, PollDaddy, and VaultPress products.
In the end, this doesn't appear to be a particularly different product from other large services such at Github, Twitter and Facebook that offer such capabilities. WordPress.com does have tens of millions of users though, and I personally would be more comfortable leaving my logins up to WordPress.com than other third party services that wouldn't be as concerned about how they interact with WordPress.org based websites. So for certain niches (like Post Status would be a perfect example) this could be a great option for simpler login / register features.
The API seems simple. Any medium-level developer will be able to understand and easily integrate WordPress.com Connect — at least from what I can tell based on the Docs.
The big unanswered question is whether this will catch on. I'm also a little confused why Gravatar isn't listed as part of this. Or maybe it is? It seems it would've been the most obvious service to advertise as being compatible with WordPress.com Connect, since it's already the default avatar service across so many platforms.
I'm also curious whether this will end up as a easy to enable feature of Jetpack, or if WordPress.org users will need to follow the developer docs like any other website or app. It makes sense to me that it'd be built in to Jetpack soon.