I just sent my Glock 20 in for the firingpin/triger group upgrade.
I was not notified about the availability of this recall, er upgrade, except by reading here about it.
The problem, as I understand it is that early Glocks use carbon steel firing pins which can corrode, causing a sticking which can lead to a slamfire.
Replacement of the pin, which also incorporates a new safety interlock, will alleviate the problem.
Glock was excellent about handling the situation, and I had the gun back within three days. They even replaced my aging slide spring with a new captive guide rod setup, which I considered awesome.
I would suppose that all Glocks with carbon steel firing pins would be subject to the upgrade. You can determine the type of firing pin you have by disassembly. Also look for a second groove cut for the ancillary safety.
The other slide rail breakage issue has to do with the bending of the particular rails. Some Glocks were fitted with rails that were bent too sharply, not enough radius. Sharp bends in any kind of material create a weak point, where a crack is easlily able to form under stress. On newer models, I've even heard that Glock has increased the length of the rails to add a larger safety factor. I've heard that certain LE agencies are allegedly pressuring Glock to retrofit all short rail Glocks with new receivers. If it happens, I'm sure that it will be a case by case upgrade with a very low profile.