As WordPress and most of all BuddyPress is becoming more and more social, there SHOULD be a way in WordPress to post from the frontend.
I wrote a plugin for this(One Quick Post - http://wordpress.org/extend/plugins/one-quick-post/), but I think it should be developped really further.
Basically, my idea was that this should be able to
-handle custom types & taxonomies
-allow guest posting (mapped to a "guest" user); with a secret key to allow the user to edit his post later
-load any meta box from the backend, so it would have to be registered only once and could be called the same way by the frontend or the backend.
Some filters could remove/add specific stuff for the frontend.
-allow to "split" the frontend edition/creation in several steps (eg. 1) post title + description / 2) post categories + tags / 3) custom fields); so it would be easier for the user to follow the creation process
Lots of people are waiting for this feature !