"Note that the Pi may struggle to power the servo and it may cause a low-voltage situation, so it's best you power your 5v servo from an alternate source (I just happen to have a few powered-up Arduino's nearby all with 5v pins accessible). Also note that even though the +/- of the servo is 5v, you can safely connect the signal pin on it to the 3.3v GPIO on the Pi as on the servo, the pin is input only (ie. it doesn't feed back to the Pi)"
I think it'd be a good idea to epmhasize this early on, in addidtion to causing the pi to freeze/bounce (hitting lower than 4.7v IIRC), powering an inductive load from the pi directly can cause a voltage spike to flow back on the 5v rail, I dare say many a pi has been fried this way :) Use of decoupling capacitors can negate such problems. Safety first and all that. Keep up the good work.