introducing: myself!

[Mux213]

Right, that sucks... Tried heat? Heat always works...

What also usually does a trick, if applied very carefully, is to put something in the cylinder so the piston can't move to far out (maybe put it back in place without the pads but with the old rotor and put a piece of wood in), but it has room to move, start the engine, and press the brake. The force the brake system puts on the cylinder usually is enough to budge it loose, but you have to be carefull the piston doesn't shoot out. I once 'fixed' a rusted volvo caliper that way

[Ivan141]

If a caliper gets stuck, take it off and rebuild the whole damn thing.. It will only get worse and you'll wreck the pistons sooner or later if you dont fix them. Doesnt affect braking performance though, it's probably the handbrake mechanism that gets sludged up or something, causing it to stop the piston from going back in far enough.
Using special tools will prevent unnecessary damage to the piston, most other tools will leave all kinds of marks on the piston, especially of it is really difficult to turn.