I know SmashWiki and ZeldaWiki at least are being hammered. Having looked at the spam pages, there's a common link that can be blocked. If the wiki owners add $wgSpamRegex = "/SESS_/"; to LocalSettings.php, it will at least block the current set of spam pages.
We added that at Nookipedia a few hours ago, and it seems to be working. I'd recommend that the other wikis add this as well. Thanks for posting this here. :)
No problem. Just watch - it won't stop them signing up, just block the template they've been using from being saved [i.e., it's a band-aid to buy time for more permanent solutions rather than a final fix] :)