Well.. I don't know if central piwiki system for external wikis is
legal in all jurisdicitons, especially in EU as it means transfering
personal data to third party abroad. At least - pages using such
external piwiki instalation should warn their user that their IP, date
of access to webesite and browers user-strng is about to be recorded
by third party... It also apply to the website which decided to use
google analytics or any other such a system not installed on local
server.