Check your brake pads if you think they are down...

[Steampunk]

Long story short (NOT on my MX-5 just for the record), but the "squealers" on the pads on my other car failed to do their job.
After a week or so of driving with a slight, occassional, grinding noise, I removed the pads on the side that was making the noise; one pad was down to the metal backing-plate, whilst the others had approx 1mm-1.5mm of friction surface remaining.

This is the first time that squealers failed to warn me, I never heard the slightest squeal from either side.

I always do a quick engine-bay check every fortnight, and kinda pre-empted this as the brake fluid went down to the half-way mark, but was still expecting the squealling. Oh well.