Twitter is currently acting as a write-only medium, from the perspective of applications.
in Twitter: The missing feature I talked about how Twitter acts as a messaging bus. However, while I’ve found plenty writing to the bus, I haven’t found many applications take advantage of reading from the bus. That is, the twitter feeds of others are rarely used in a particular context.
For example, I’d want all incoming bookmarks in my twitter feed to be converted into delicious bookmarks so I can read them later. Packratious does that for me. However, you’d think that other things, like events management, photos, etc. could all be managed by websites outside twitter by listening to the twitter feeds themselves. If you went to youtube and saw a “Here's what your friends have been watching”, or flickr and said “here are photos your friends took” or even delicious and “here's what your friends have been linking”.
Shocking really, that these sorts of features aren’t available right now.