The changes are mostly things that streamline the site. Things such as extra spaces between the lines, extra icons and stuff that showed up, and extra headers. You might not be able to tell since the changes were made to make this IPB installation more like the PunBB installation earlier. Also, instead of three lines per forum, it only uses two lines now.
Oh, and there used to be a big Invision Power Board logo at the top but that's gone now.