Kimber II
I can only post about what I know. I bought a Kimber Pro Eclipse II almost two years ago (I think it was Christmas 2001). I was leary about the series II safety, but the gun looked and felt so cool in the store that I decided to buy it anyway.
It's been a great gun and I haven't experienced any series II failures. I had sold a Colt XS Lightweight commander to buy the Eclipse. The Colt was nice, but too light for marathon shooting sessions (should have kept it in hindsight for collector's value). I prefer the Kimber to the Colt I had. It shoots point of aim, and is much more accurate than the Colt. Also, the Colt's slide would routinely fail to stay locked open after the last round was fired when I used the factory provided 8 rounder. The kimber didn't have this problem unless the gun was pretty dirty (250 rounds or more without clearning). I use a standard 7 round mag and haven't had any problems with the Kimber, even though I haven't replaced the recoil spring (the factory recommends replacing it every 800 rounds - I'm probably close to double that in the round count). In fact, this past week I was shooting the Kimber and I was able to feed and fire some Magtech 230gr ball rounds that had jammed up a Colt S70 MKIV 1911 that I had. The rounds were shorter than a standard round (because of the way they jammed in the MKIV), but in spite of that the Kimber Pro fed them with little or no problem. I was surprised.
I think that the Series II safety is pretty effective from what I've experienced. I was totally leary about the system when I first got it (I shot the gun upside down, sideways on both sides, etc., trying to get it to jam), but it seems like it works well. As with any mechanical device, I wouldn't be surprised if there are examples of Kimber II's that have problems with this system, but I personally think that if the system is installed/adjusted properly, it works very well.