I'm resurfacing/trimming my rotors, do I have to replace my brake pads too?
Yes you should. The price of new pads (in most cases) is small $$. This will get you fresh mating surfaces on both sides. If you don't, you run the risk of screwing up your fresh cut on the old rotors. Don't forget to correctly bed the new brakes after installation or you run the risk of being back at square one.
Pads and rotors should be considered a consumerable item. Forget about re-grinding the rotors. If you are on to your second set of pads on your rotors, drag your thumb nail across their surface. If your nail can feel any grooving or catching, change the rotors and the pads.