Seating orders effect on Puerto Rico
Seating is very important in Puerto Rico.

The seat that wins the most is 1st Corn (based on World Boardgaming Championship stats).
Here's one of the tourney pages with stats, if you look around you'll find more.

Here's the compilation of stats from 2002 to 2009:

Seat 1 indigo 41.53 scoring average, 19.9% of wins
Seat 2 indigo 40.73 scoring average, 19.5% of wins
Seat 3 corn   43.48 scoring average, 30.8% of wins
Seat 4 corn   43.35 scoring average, 29.7% of wins


Having corn allows you to produce sooner, and more, so you can make more points shipping.
It requires less men, so you can do more with the men you have.

One of the big reasons that it gives an advantage is that it's a simple strategy, just make corn and ship.  The other strategies take more thought and hard decisions.

One other factor that comes into play in Puerto Rico is that you have to change your tactics and maybe your strategies based on the player to the left and what he does.