I just replaced my front pads last night and one of those thin, hook-looking silver clips came off when I was putting the pad in. Is it a big deal if it's not on there?

Thanks!

 

If you mean the "clip" attached to the back of the brake pad itself, it's most likely a wear sensor which squeaks when contacting the rotor to alert you your pads are getting low. If that's in fact what you mean, I wouldn't be too concerned about it.