The iPad announcement generated 177,000 tweets in the first hour

"It should come as no surprise that the Twittersphere was (and still is) all a-buzz about the iPad — the build-up to which has been months in the making — but the iPad averaging nearly 3,000 tweets per minute in the first hour is just plain remarkable. We haven’t seen anything like it in recent history. According to Trendrr, tweets did taper off a bit after that first hour, but are still coming at about 75,000 per hour, or 1,000 per minute."
Data from Trendrr, reported by Mashable, 27th January 2010