What kind of statistics should I run on a database? I have written a python script to verify the strategical rule of "controlling the center". 

I have parsed the free 2.2 million games database (it takes about 5 minutes) and I have found that the winner of a game controls the center at any given time with (on average) 1 more piece than the losing side.

I'd like to look at the correlation of other strategical principles with winning. What would you suggest would be an interesting list to look into?
(I'm thinking of castling vs no castling, knights on the rim...)

EDIT: I would like suggestions for interesting statistics that you would like me to run. I could then send an article (say, to chess.com, or TWIC) with the results, referencing the suggestions posted here.
To extend your center squares analysis, it might be interesting to determine the expected winning percentage in the database when one side has 0, 1, and 2 pieces on average central square advantage.  This would begin to show just how important the advantage is as I would think the winning percentage would increase as the advantage becomes more pronounced.

Also, a knight on c3 covers two central squares e4 and d5.  Are you counting the number of times the central squares are controlled or are you counting just the knight on c3 once?