Having had a chance to play around a bit with #newnewtwitter, two changes strike me as particularly interesting, one is a small change in mobile browsing and the other focuses on anonymity. It seems to me that they are both changes designed to alter users' behaviour.
Placing Twitter at the centre of mobile browsing
On the updated iPhone app you can no longer copy a link and paste it into a browser. This means you have to browse through the app's built-in browser. Facebook's app takes a similar approach. It means that if you want to view the content someone is trying to share, you need to do it through Twitter and without leaving Twitter. So you stay on Twitter, it acts as the hub for your mobile browsing.
When you couple this change with Twitter's new discover tab (an amalgamation search and trends with a new stories service), it's clear that Twitter is making a serious play to challenge Facebook and Google as people's starting point when exploring the mobile web.
Nudging people away from anonymity
Names now take precedence over Twitter handles. Is this a way to make online relationships more personal? Is it a small change in the larger push to make Twitter big in China and other countries where the government has a preference against anonymity? Or is it a move to placate Western governments who, now feeling some pressure of movements organised through social media, are less enamoured with free speech when it's coupled with anonymity?
Regardless, one thing it will definitely do is make users associate people by their names instead of their Twitter handles. This means that, unless you're writing under a pseudonym, people will associate you with your tweets. It won't be @quirkytwitterhandle said something, it will be Trevor said something.
Obviously, there are easy workarounds to this change, for example you can change your name in the settings to your quirky Twitter handle. Most people won't do this though and, over time, this will change behaviour. I suspect people will moderate their tweets because they will recognise that those tweets are directly associated with them instead of their chosen online identity.
So, two very different changes, but both designed to change behaviour and both more significant than they initially seem.