Taking apart the SIXAXIS is straightforward. There's a clip holding the shell together in the middle, between the two analog sticks. It's part of the bottom half, so pressing there helps.
Putting it back together can be a bit tricky because of all the parts moving around that have to get lined up just right, but it's not too bad. The pin attaching L2 and R2 can slide out easily; try to keep it in place, because replacing the springs can be hard if it all comes apart.
If you get everything back together and the controller doesn't turn on, make sure the the battery is connected, and ensure that the power-off button on the back of the controller (through the pinhole) isn't being accidentally pressed.
The four indicator LEDs on the sixaxis are surface mount parts (look to be around 0604 size) and are brought to the front through light pipes. I plan on replacing them with red, green, blue, and yellow.
There is an empty pad labelled LED5 directly under the PS button. There's a diffuse lightpipe leading up to the button, so LED5 is just begging to be stuffed. I'll probably put white here.