Well, I've done quite a bit more work on the serial servo controller. I've finished implementing the pin/timer interrupt combination for handling incoming RS232. The method works and has been successfully incorporated into the servo control code.
Note to self: "Interrupt flag bits get sent when an interrupt condition occurs regardless of the state of its corresponding enable bit or the global enable bit, GIE." - taken directly from the PIC data sheet.
I could have saved mucho timeo by reading that in the first place. :)
Unfortunately, the servo still jitters occasionally. Even when turned off. Obviously, this shouldn't happen. I'm off to more troubleshooting...