I give Twitter a lot of credit for rolling out their new Activity Stream.Sure, it's quite ugly... that can be fixed. And sure, it's a glorified newsfeed / timeline... but it's core to Twitter. A few thoughts:
1. Twitter, like many mass services, has a findability problem. In May 2008, I wrote that Twitter's problem was social findability. This helps.
2. The web is based on Ego and this certainly feeds to the ego. It answers in real-time what's happening around ME. That's powerful & addiction.
3. I can Twitter becoming two primary streams: tweets and activity. For publishers, activity could be a more powerful hub. For individuals, the normal stream probably is.
4. For publishers and brands, this could become the first step towards a publishing dashboard. The foundation is being laid.
5. It's ugly. Needs serious UI overhaul. Twitter is usually so elegant and simple... surprised by the visual experience here. Again, it's easily fixable.