If you want to plug shields on top of this one, make sure you pick up a set of shield-stacking headers
http://www.adafruit.com/product/85
and solder them instead of the male header

Since this shield only uses the I2C pins and the I2C bus is sharable, you can stack multiple shields on top of each other. You will need to have installed stacking headers & right angle 3x4 connections for it to physically connect. Multiple shields (up to 62!) can be stacked to control still more servos.

You may have difficulty with the 'left-most' header since we updated the transistor to be beefier. Use the 3 ports to the right or solder wires out to get mechanical access

Addressing the Shields

Each board in the chain must be assigned a unique address. This is done with the address jumpers on the upper right edge of the board. The I2C base address for each board is 0x40. The binary address that you program with the address jumpers is added to the base I2C address.

To program the address offset, use a drop of solder to bridge the corresponding address jumper for each binary '1' in the address.

Board 0: Address = 0x40 Offset = binary 00000 (no jumpers required)
Board 1: Address = 0x41 Offset = binary 00001 (bridge A0 as in the photo above)
Board 2: Address = 0x42 Offset = binary 00010 (bridge A1)
Board 3: Address = 0x43 Offset = binary 00011 (bridge A0 & A1)
Board 4: Address = 0x44 Offset = binary 00100 (bridge A2)

etc.