Version 3.0 of Posterous has hit both iOS and Android adding in Spaces to both, but unfortunately the Android experience is pretty gimpy. On iOS you can not only create Spaces, but add in various accounts to autopost on public Spaces. Also on iOS there are new tabs, including the Reader tab, which gives you quick access to view and comment on posts from people you're following; a Popular tab to allow users to find interesting Spaces to follow; and, an Activity tab to get at your comment stream.
On Android, you can't do anything more than view posts in a Space, post to a Space, and create Spaces. There is no reading list or comment stream, no popular list, and no option to add autopost accounts, or even to find your friends on the service. So, if you're on iOS, definitely give the app a try, but if you're on Android, it may not be worth your time. Of course, it all boils down to whether or not you even use Posterous, which has the worst issue a sharing network can have: a lack of users.
Posterous is available for free in the iTunes App Store and the Android Market.