About a month ago I installed OSQA and 'shapado' -- http://shapado.com/ QSQA appeared much more rounded compared with shapado, and behaved much more like StackOverflow. Only problem I have had with QSQA is that changing the theme / template could be easier.

Oh, and by default the admin page of QSQA had a strange almost intelligible layout. However this is a mode that can be turned off... Once you find the option.

QSQA also has a neat 'community bootstrap' mode that lowers the required reputation for many actions, linking URL's down votes, etc.

All in all very happy with QSQA.