I suspect the hopping categories was to try and buy time to calculate what sort of questions would be asked in each. But it's first move of getting into the lead (and the daily double) I would say is a combination of good strategy and PSYOP.
It looked like he went to the 4th row to find the daily double, then just went through all the cheapest questions, as he was most likely to answer those. He finished all of the $200s, then went to the $400s, etc. I don't think it was to trip up his opponents, I think it was to have a better chance at answering.
I thought Watson was searching for the daily double spot to jump ahead $1000 right away.
And also to steal the humans their chance for a late comeback in the game.
oooh, good strategy.
The daily double is equally likely to be under any unrevealed spot, so jumping between categories has no effect on the probability of hitting it.
Ok, this is wrong. Ken Jennings said in an interview that the DDs are more likely to be in the bottom rows, so you actually can hunt for it.