[apowell]

MSN.com will often include direct links to Bing searches relevant to articles or news items. If you rank well for the linked term, then you'll see a traffic spike. For me, the pattern has been a massive traffic spike for a single keyword which trails off for the next twelve hours or so.

This doesn't sound like what you experienced, but perhaps it's a helpful clue.

[kongqiu]

That is good to know; thank you for sharing this.

The spike I saw was across many different keywords and content areas, but only lasted one day.