I have updated some homepages to the brand new mediawiki version 1.13.2 which was very easy. They have a very good description what you have to do, if you update to a new version and a very nice update script which works also for very old wiki versions (I have tested this with the 1.4.5 version).
But there ara small problems with own skin (for example on http://www.buzztard.org). The skin have to be fixed per hand. Hopfully ensonic can do this the next days.