The big fat search box. What else?
Internet Explorer 8.0
This will be fixed in the next build, with one exception: the layout will be slightly different in IE8/Compatability mode in that there may be no space between the box at the button, but all other browsers will render this
This is a compromise in that it's 98% correct in IE8, looks fine, works fine, but differs visually slightly...and doesn't involve lots of extra CSS for a 100% identical layout, given all other browsers handle this situation fine.