Hi,
Its better to use a dedicated power source for your Arduino (as you are) and another dedicated power source for any power hungery devices such as motors and servos.
In some recent test I ran, the Arduino drew 10mA current whereas a single servo could draw upto 1.5 Amps at stall.
See here -
and
Notice the effect that the servos have on the quality of power, its best not to have that running through your Arduino.
Duane B