I must step in here to correct some mis-information.

There is no such thing as "shift" with regard to ESCs or servos.

"Shift" refers only to compatibility between transmitters and receivers. A positive shift transmitter requires a positive shift receiver. A negative shift transmitter requires a negative shift receiver. Futaba and Hitec are negative shift. JR and Airtronics are positive shift. Many modern receivers auto-detect the shift and so are compatible with either system.

ESCs and servos do not have a "shift." Except for some old Airtronics equipment, all ESCs and servos have the plus (+) wire in the center pin of the connector, with the minus (-) and signal wires in the two outer pins. The modern design, with the plus pin in the middle, means you can not damage your equipment by plugging in an ESC or servo backwards.

Different manufacturers use different wire colors and sometimes slightly different connectors, but the order of the wires is always the same: plus in the middle pin, negative and signal in the outside pins. Here's a thread that illustrates the ESC/servo wire colors for some popular manufacturers:
[link=http://www.rcgroups.com/forums/showthread.php?t=392644]Servo connector compatibility[/link]

Today, nearly any ESC or servo will work with nearly any receiver, though the connector might need slight modification. Just don't try to plug an old Airtronics servo into a modern receiver!

- Jeff