I lost a key to my oldest Kryptonite lock, circa 2000. Got on the Kryptonite website Monday and ordered a new key for $6. It arrived today and works. All I needed was the other key for the serial number on it.
I've had two locks replaced by them after thieves caught on to the weak points of that generation. That wasn't much harder beyond having to go to the post office to send them back.
I'll buy another when the time comes. Don't know when that will be. Three locks suits me well and none seem ready for replacement. (They do benefit a lot from occasional doses of wet Finish Line lube as my bikes are often ridden and locked in the rain.)