I was thinking of getting silicone pads for baking cookies on, as seen on Martha Stewart all the time. They make baking dishes and spoons too. Does it leach into food?

No, I have never seen any evidence of this.  And there should not be anything in silicone to leach.  I made some one time by accident working on another experiment.  Pretty simple actually, react sodium silicate with an alcohol.  Silicone does not need plasticizers that leach like plastics.

Reminds me of the silicone breast implant question of leaching. I'm sure there are other prosthetic body parts made of silicone also, like joints.

This was actually leakage both by ruptures and migration through the silicone sack.  Exposed to the immune system the body does create antibodies to the silicone, which is why women with silicone implants can end up with autoimmune disorders.

How dangerous is silicone?

I don't see it being a safety issue with cooking.