Dave Zatz blogged this morning his experience on a Southwest flight returning from CES last week.
He used Southwest’s wireless service to access his Twitter account. Someone else on the plane accessed twitter from their computer and found they were logged into Dave’s account. As Dave notes, if this had been done via sidejacking the intruder would have likely been a lot less mature. Instead they just posted one message to the twitter account indicating they were there.
As he notes, this is more likely caused by a caching proxy. Frequent readers will recall I had a problem similar to this at work two years ago.