Twitter’s new design is about to be rolled out as covered elsewhere. It involves quite a major redesign that includes multi-column layouts and inline media. Quite simply it looks a lot like Facebook now. Since Facebook initially made their interface more Twitter-like this brings it full circle. Media is still hosted on external sites so this means that external sites will get a lot less click throughs for the same bandwidth costs. Although Twitter did work closely with these partners it remains to be seen how this will affect their traffic and revenue. Sites without any added value will probably be eventually rolled into the mothership or collapse.
The new design iteration is long overdue and something that will benefit the typical user. One of the only features missing from desktop apps and other applications is the ability to switch between multiple accounts.
Aside from ironing out kinks and subtle adjustments, Twitter clears the way for enhancing their advertising platform. The increased visual noise (or activity depending on how you see it) will give them more leeway to introduce more advertising into the mix, not to mention a healthy dose of page views and ability to retain more users on site.