just to clarify, when I said you can use as many as you want I was talking about pneumatic cylinders. as for motors, you are limited to those in the kit, including servos (as everyone has already said).
Well, FIRST changed their defintion this year (which is why I suggested asking FIRST).
Q: Are servos treated as electronics (in which case we can have an unlimited number of them) or are they treated as motors (in which case we are limited to 2)?
A: Electronics.
In past years yes, this year no.
Refer to rule R54 third bullet in the robot section of the manual:
“There is no limit to the number of solenoid valves, air cylinders, and connecting fittings you may use on your robot. They must, however, be “off the shelf” pneumatic devices rated by their manufacturers for pressure of at least 125psi. Besides the “free” pneumatic components listed on the Pneumatic Components Order form, you may use additional air cylinders or rotary actuators, however, they must be identical to those listed on the Pneumatic Components Order form, and obtained from a Bimba or Parker Hannifan distributor.”
Just wanted to get thing straight 
See Team Update 6, since FIRST corrected themselves again. You may only use the 2 servos in the kit.