You may already have tried the new Twitter, I have with one of my accounts. I have to say that it is completely different! Well... the tweets are the same and your followers and people you are following... and the messages will be the same. I'm talking about the style and the way things work. It took me a week to get used to it.
The biggest change is the width: it's twice larger! Yes, twice! (well... at least the right column.) That means the Tweeter output will fill most of your screen up. I suppose that they will keep the smaller view available for cell phones. But on my desktop, that's just plain BIG. In itself, it's not a problem, you get much more info on the screen. But...
The result is that now your background image will "break" (Our Snap! Websites Twitter background is shown on the left, see the result in our screenshots below.) Most people won't see much of it anymore when they are on the new Twitter. Although it is still there, unless the users have a really wide screen, but don't count on it. It will need to be changed...
On that one, I'm wondering how much research Twitter has done. It may be part of their plan of adding advertising interleaved with your tweets... (which I thought they started, but so far I've not seen any of those commercial messages anywhere!) So getting your crap out would be a good side effect. (This is really my total speculation and I'm probably wrong... )