On May 15 my site SpamOrHam.org was mentioned in a story on the front page of Slashdot. Up until the moment when a link to the site appeared on Slashdot people had been visiting the site and classifying about 100 messages per hour (that's period A in the chart below).
All that changed at 1530 GMT on May 15. In the first half an hour (until 1600) around 3,300 classifications were made (an increase of 33x). Point B on the chart is the peak of 9,803 classifications in an hour that occurred during the hour starting 2000 GMT. By this time the story was no longer number one on the Slashdot (it was demoted from the number one spot at 1628 GMT).
At point C the site dropped from its peak classification rate, this occurred nine hours after the story first hit Slashdot. Those nine hours correspond to 0700 to 1600 in California and 1000 to 1900 in New York; peak working hours in the US.
The second significant peak occurs at point D occurred 22 hours after the story hit Slashdot; that corresponds to 1100 GMT on May 16. During this period the US is sleeping, but Europe is awake and working.
There's a smaller peak that I've labeled E which occurs 16 hours after the story hit the front page. That's 0500 GMT which just happens to be 1500 in eastern Australia and similarly the middle of the afternoon in Asia.
Happily although the site is no longer on Slashdot, classifications remain 5x higher than before it was mentioned.