What is the average number of thoughts per day?

Lots of this answer depends on what you consider a thought.

Is a thought:

• a new idea
• a nagging question
• a worrisome situation
• a recollection or memory
• a surprise

Some scientists define brain 'action' by way of synapses -- the "...conducting link between two abutting neuron cells." The time it takes for a synaptic transaction to occur is between 0.2 ms and 2 ms (thanks to Wikipedia).

This would be an interesting experiment to quantify and perform.