It seems that some people are having issues with the new 1.2 system update for N9 failing at 0%. The problem has been identified (see comments by Santtu Ahonen at Nokia developer blog) to be caused by configured repositories that cannot be reached. The issue is NOT caused by MeeCatalog and MeeCatalog does not by default add any repositories.
If you have added custom repositories via MeeCatalog settings it is advised to disable them and refresh the catalog lists (the button in the middle of the toolbar on MeeCatalog) before updating your system software. Note that you cannot disable repositories added by other applications using MeeCatalog.