Until recently, my highest was 20. I was Turkey, ended up racing to the win against England, who ended with 14 when the game ended in 1908. I started allied with Austria to fight Russia, and while Russia and Italy invaded Austria, I grabbed some of Russia. When it was clear that Austria was going to fall, I finished him off as quickly and painlessly as possible. Then I allied myself with Italy once Russia had fallen, but I occupied the entire Mediterranean. We took down France together (imgaine, Italy and Turkey allying against France) and then stabbed Italy for the win.
But now I'm in a game that is about to enter Autumn 1911, which will be the final turn. I'm playing as Russia, and Turkey and I played a classic Juggernaut as we steamrolled across the board. At the end of 1910 I was sitting on 17 centers, Turkey was at 13, and Italy (which Turkey had been unable to squish) was at 4. I figured that since it was a points per supply center game, I might as well go for as many as possible, so this spring I grabbed Spain, Vienna, and Ankara, leaving me with a pretty little 20 centers. Turkey, however has been NMRing the past few turns, and if he does so again, I'll pick up Spain, Marseilles, Venice, Trieste, Romania, Constantinople, and Smyrna. 27 centers.
So what's everyone else's high center score? I think I'm setting the bar pretty high with 27, but I'd love to hear what others have gotten.