Is there any reason why the perchlorate found in Martian soil couldn't be used by living organisms?

Martian soil apparently has a lot of perchlorate salts in it. When this was discovered, a lot of commentators said this was a problem because perchlorate is toxic. As a chemist, I think perchlorate would be an excellent source of energy for lifeforms. It's kinetically stable but thermodynamically unstable - perfect for an energy source. Just because earth life prefers abundant oxygen as the oxidation source in biochemistry doesn't mean something could not have evolved to use perchlorate. I guess finding both perchlorate and a reduced oxychloro anion would be a strong signature for life.

OTOH, the perchlorate concentration may be too low for this to be practical.