I asked this question yesterday, approximately 18 hours ago ("2011-12-13 20:24:03Z" according to the hover text), and it's still being displayed as "today".
I assume the "Z" in the timestamp refers to Zulu time, so I converted my current time to Zulu, and the date (2011-12-14) differs from the timestamp on the question.
I don't pretend to understand all of the complexities when converting time zones, but I thought it was strange enough to report. If it matters at all, I'm in US-Eastern.