We have version 4.6.2 and 4.6.3 installed in different sites, and just noticed that the new Reports tab interface UI is broken. You can click on the tabs but the main body of the report settings - columns, grouping, sorting, filtering, etc - is always visible just as it was in older versions.
I've checked the official demo site, running 4.6.4, and it looks OK there. I also have a dev site on my local machine running 4.6.1 and it's OK there too. Seems unlikely to me that this was broken for 2 whole "dot" releases. I've cleared caches on Civi and Drupal.