Look ma! - I killed Chrome!
Before you ask:
1. Yes, I do want a medal
2. Yes, I realise this is probably not an uncommon occurrance given Chrome's been out in public for a week or so.
FWIW one tab had a fullscreen PDF (URL points directly to a PDF file, no embedding inside HTML). Not sure what the other tab was up to.
Also: The "fullscreenness" of the PDF was questionable - Chrome seemed to be unaware of where the window borders were and just stoicly kept refreshing the plugin at the same resolution the window was at when the page loaded.