You can search RC using their built in Google RC search:
http://reefcentral.com/search.php?menu=11
You should find more than you'll ever care to know about on the subject
Basically the advantage of the center overflow is that is skims more of the tank water as it is 3 sided vs the 1 side of a corner overflow. The nice thing about a corner overflow is that it is easier to aquascape around and easier to DIY.