I agree with all posted.
The caps plugged into the receiver can help retain responsiveness from high torque or high speed servos, as well as help to eliminate receiver shut down's from insufficient voltage.
This is especially a problem using the Quatum Comp/comp 2 ESC's as they have a low output current (only 1.4 amps). Good servos can use that up alone.
And, to compound the problem, the regular Spektrum receivers are sensitive to this low current and will not operate properly WITHOUT a cap plugged into it. I found this out right when the Spektrum first came out. I could NOT get mine to work, then I tried the cap plugged into it and it worked fine.
The other alternative, if you are running a PT as well, is to construct a 6volt/2 amp regulated output device to power either the entire receiver/servo/PT system, or as I do, just power the servo. That way I know my servo is getting 6 volts, and plenty of current is available for it. And my spektrum runs fine off my BEC of my QC2 with the PT plugged into it. You could also use this device to power the personal transponder.