We stewards and [[m:SWMT]] members regularly have to fight cross-wiki vandals
who vandalize a page and all the pages interwiki'd with it. Blocking the vandal
on one wiki is useless because he makes only one edit on each wiki: he
vandalizes the page and then proceeds to the next page in the interwiki list.
All we can do is follow him through interwikis and revert.
I'm only talking about IP vandals in this case, because such vandals don't
create accounts on each wiki they vandalize.
For the moment we haven't got any tool to deal with this kind of vandalism. A
kind of "meta-block" would be very useful.