I've been watching this thread with some consternation as have never worn through a set of discs since I started driving in 1988. This includes several thousand miles of towing. Naturally cars have arrived with worn or corroded pads / discs and they are attended to, but after that, no, they just run and run. I should say perhaps that I live in a hilly area and few of my miles are of the relaxed motorway sort.
So ... I do use 'decent' brands, so TPS economy brakes (which are fantastic), Pagid, Ferodo or Brembo. Usually whatever I can get at the time.
I have a feeling that nearly all of the above issues are down to calipers not releasing fully. If you're not getting a good 20-30K out of a set of pads on a manual car, let alone discs, something's horribly wrong. This may be mechanical, or in some cases, dare I say, driving style. Let's assume the former as obviously we're all perfect drivers on here.
A few things: if a front caliper is happy, there should be no friction at all when the car is jacked up and the wheel turned. The design of the piston seal is such that it slightly grips the piston and retracts it a fraction once the brake pedal is released. The slider rubbers do the same. The sliders should allow the caliper to slide easily enough that if you retract the piston a fraction by levering the caliper over a touch, you should be able to slide the caliper by hand (no leverage).
The pads should be able to slide by hand within the caliper: if you need to lever them, they are too tight.
Common faults on the actual caliper:
i) Corrosion (rust) up behind the caliper bellow seal, pressing the bellows hard onto the piston. No amount of levering piston back and forth will deal with this.
ii) Ditto for the main piston seal (the square section one).
iii) The piston itself is corroded.
All three will leave a piston that is unable to self-retract. Therefore, when you come to a halt you have a very hot disc with pads clamped hard onto it in one place. This means one area is cooling at a completely different rate to the rest, leading to warped discs and a pulsing when the brakes are applied, especially lightly.*
Cure for all three is the same: get a drip tray, remove the caliper but leave it connected. Pump the brakes gently until you feel the pedal suddenly go soft. Gently press the pedal all the way down and wedge it down with a bit of wood between that and the driver's seat: no more brake fluid will come out. Remove the piston from the caliper, working it out from the bellows. Remove the bellows carefully by collapsing it inwards. Some designs are held in with an spring clip. Use a hook tool or tiny flat screwdriver, lift out the square section piston seal. Clean seal and bellows: almost always they'll be fine to go again.
Use a Dremel with wire brush and plenty of WD40, clean out the inevitably corroded bellows and piston seal channels. They'll almost always release a ton of rust: keep going until they are bright again.
1500 grit the piston using WD40 and polish. Not a huge issue if the last 5mm or so is a bit pitted, but replace if the pitting encroaches upon the seal.
Give the inside of the caliper a good spring clean: ideally brake cleaner, but WD40 will do, you're cleaning it all with some clean rag / paper towel anyway. Make sure it's clean, dry and debris free: use a torch to make sure.
I should say, it's very satisfying at this stage: rust has all gone, inside of caliper is lovely and clean and you have a little row of seals / piston all ready to go back in.
Lollop red rubber grease into the piston seal channel and refit the seal. Refit the bellows, again on a bed of red grease. You should see both will sit right into the channels now.
Now the tricky bit, red grease the piston and try to get one 'side' into the bellows and then try to work the other half over the piston. This is the worst part of the whole job. I've got various little blunt hooky tools I use to ease the bellows over the piston. This done the piston can be eased into place in the caliper. You may have to wiggle it a bit but it will start to slide in eventually. If you've done all of this O.K., the air pressure will try to push the piston right back out: that's how free it should be.
O.K. , that's the piston area, there's another area of potential issue: the pads. With the pads and anti-squeal shims out, file up any area of caliper that contacts either shim or pad. Corrosion often builds up under the shims unseen, clamping the pads in place. Reassemble using Copper Ease or similar under the shims to slow future corrosion. Do a quick reassembly and try sliding the pads: you should be able to move them with a finger: so not rattling loose, but an easy slide. If they are tight, gently file the very ends where they contact the anti-squeal shims. Refit with some anti-seize of some sort (Copper for cast steel / iron, white for aluminium).
Once re-assembled, bleed the brakes. Be aware that if you've fitted just new pads, any disc ridges on inner and outer edges should be nipped off with flap disc in a grinder or even with a file. You may find that if you use new pads on used discs (perfectly acceptable assuming discs will go again) it may take a few miles for the brake pedal to finally firm up. This is because the give you are feeling through the pedal is often the new pads flexing slightly as they try to match to the disc.
As is usually the case with my little interjections, note the total cost of my caliper clinic is in the region of £5, assuming discs and pads going again. A couple of Dremel wire brushes, a dab of copper grease, a splash of brake fluid and some elbow grease (priceless). I've had a little practice I'll admit, but could probably do the front end of a car in roughly 90 mins all in. Allow a couple of relaxed evenings or a weekend morning if you've not done it before and you'll be fine.
Key thing is to make sure the road-wheel can spin perfectly freely: ideally just after someone has stomped on the brakes with the engine running. That's the greatest test and replicates actual driving.
*On trackdays / racing, you never apply the handbrake when parking in the paddocks post session: you always put the car in gear or chock the wheels. This helps to prevent warping.