OAuth support for user authentication
This is by the far the most important feature and is really a core requirement for any application using the posting API.One of the big problems when I built Ringerous was that it required every user of the service to give me their password. I have to post on their behalf on the backend so there is no way to prompt for a password while the user is using the app. Giving up a password is a tall order. OAuth makes this problem go away.
A search API
Content is king. But only if you can find it. Posterous is a constant stream of great new and timely posts. For applications that are not revolving around a single user, a search API is needed.
A public timeline feed
I'd like to see Posterous add an "explore" call that is equivalent to http://posterous.com/explore/ which is available via the web today.This page is a fun way to explore the diverse body of content being shared every minute by the Posterous community.
A user subscription feed
Similar to the explore feed, it would be nice to provide an API call for the user subscription feed so it would be possible to present a user's Posterous network of blogs.
Enable granular control for autopost
Currently, the autopost feature is either on or off when posting through the API. Just like email, there are use cases where the user may want more control over the services being updated. It would be nice to provide this feature in the posting API.
Hook up Posterous notification emails
This is likely an easy one. For whatever reason, the email notification system for subscribers is not hooked up for posts that come via the API. This significantly limits the communication benefits of Posterous for group sites.
Provide access to user profile data
The API is missing a user profile call. Providing access to details about the user such as description, thumbnail, and favorites adds a personal touch, a sense of community, and a method for exploring when third-party applications need to provide content navigation tools.The current API is a great start, but it is clearly geared toward mechanical tasks. It's no mystery that so many of the existing API implementations are utility tools for porting blog content from other vendors. But there are great opportunities for Posterous and its developer community to add new functionality and experiences to the platform.