I've recently had horrendous brake squeal coming from the front brakes, with a lot of brake pad dust on the near side. 
So this afternoon I've stripped it all down, cleaned everything up, filed the leading edges down and reassembled, which seems to have done the job! 
However, the brake pads on the near side have worn unevenly. Where the caliper piston is the pad has about 10mm left, but the other side only has about 5mm. The offside set have worn evenly and both pads have about 10mm left.
Any ideas folks? 
Sounds like the piston side is seized and the "other" pad is doing all the work ... EITHER the piston itself is seized, or the pad is seized in the runner/guides/pins.
To check the piston remove the caliper from the disc, and remove the pads, get someone to GENTLY apply the brakes while you watch the piston .. it should slowly ease out ... if it is reluctant, or takes a lot of pressure to move, then you can try cleaning up the fescalised (shiny) part .. which might be corroded. It can be "exercised" by gently squeezing out, then back in using plumbers pliers or similar
If the piston moves OK then check the caliper guide area for corrosion, clean up thoroughly with wire brush/scraper then apply a smear of grease to the "tangs" on the brake pads and the area on the caliper guides where they sit.
I always put a bit of silicon grease on the guide pins as well .. seems to help the movement of the pads over time..