While I don’t have any statistical evidence for this, I do believe that the “slot” allocated for a keynote or general session speaker is getting shorter. It used to be quite common to have a speaker present for 60-90 minutes. These days, it is more like 45-60 minutes and I see that trend continuing. People want more variety, and you can squeeze two speakers into a 90 minute spot. One of ‘em is bound to be great! Even better if both of ‘em hit it out of the park!