The new board interface was released today. There are plenty of architectural changes (for reasons to be announced soon), plus a number of presentation changes and new features.
As stated before, some people with older browser may experience problems, so a legacy interface is available.
From the board settings page, click the link contained below :
Note : If you are using an old web browser or a web browser with limited functionality and you are experiencing problems, please click here to select a reduced feature board type that may be compatible.
This alternative interface has reduced functionality, but if you could use the site before the upgrade, then this interface should enable you get by until you can upgrade your browser. (All current versions of most browsers should be compatible.)