Here’s an interesting measure of how effectively Apple AAPL can whip the tech world into a frenzy — even without Steve Jobs there to stir things up.

According to a report issued Monday by Nielsen Online, “anticipatory buzz” in May drew more than 55.7 million unique visitors to Apple’s website — more than double that of Hewlett Packard HPQ and 25 times the site for Microsoft’s MSFT Xbox.

The buzz got even louder in June with the unveiling of the iPhone 3GS. At one point between June 8 and June 9, nearly 0.6% of the nearly 100 million blogs, groups, boards, social networks and other consumer generated media that Nielsen tracks were talking about the new device. According to the report:

“the new iPhone 3G S sent blog mentions up 1,226 percent week-over-week on June 8, the day of the announcement. After the initial announcement, buzz dipped but again picked up after the phone became available to consumers on June 19, with blog mentions more than doubling compared to the week prior.”

You can actually see Apple’s buzz machine in action in the accompanying “BlogPulse” fever chart:

Nielsen Online is a division of the research company that has been measuring — and indirectly shaping — media content since it began tracking radio audiences in the 1930s and TV shares in the 1950s.

In the promotional material on its website, Nielsen offers the schematic drawing at right to suggest how its “BuzzMetrics” data mining service extracts nuggets of intelligence by harvesting raw data from sites like this one, cleaning it up, and giving it a good polishing with its relevance and analytics algorithms.

See also: