I don't think anything broke, just some minor problems with cookies.

If you are experiencing this on your mobile device in, say Opera Mini or similar, I suggest clearing you cache and/or cookies.

I had problems accessing the www version on my BlackBerry as twitter suddenly insisted on showing me the m version every time I accessed www.twitter.com with Opera Mini 4 - even after I had repeatedly requested the 'standard' www version.

I deleted my cookies and it is now working again.