In similar lines here are my observations as a heavy business and personal user:
1. 140chars limit had a goal and philosophy which conflicts now with image attachment flood. Most "interesting" content is typed or pictured in the attachment and the 140char limit is simply worked around
2. Twitter UI is too clunky for what it does. No progress since 7 years I'm using it.
3. Twitter mobile apps don't work properly when mobile. You can't favorite, retweet or comment properly while in an unreachable zone. My 2008 hobby Android 1.1 app has a local queue to cope with remote updates, inserts and Twitter can't implement this?
4. Families aren't on Twitter. Friends to a certain degree. Colleagues to a certain degree. Celebrities/followers yes. Gamers no. Protestors yes.
5. Facebook, LinkedIn implemented the "follow" feature quite successfully.
6. Notifications work, Discover not much.