My Mega ran 18 servos just fine.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1267069898/0
I did use an external power supply.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1265626147/6#6
I have a Watt meter at home. The robot is currently disassembled, but I am working on getting it back together. When I do, I can post the amps that all 18 servos pull when walking.