Yes I have experienced the same situation. Just the other day the wiki was down for a day and half. Since the beginning of the year it has been down at least two other times. One time it was down for the entire weekend. I complained on the participate page where you go to give feedback and suggest new features. They say that they are going to install a new upgrade based on the Xwiki 2.0 platform and that the system should be more stable. The other problem that I have is that when I click on a page it takes forever to load.