I've been riding SS Zeros for two years. They've held up well, but they do feel "loose" now compared to when I first got them. I've never come out, though, so I wouldn't call that an issue.
I've installed cleats for myself and several friends who I've talked into going Speedplay. It's not hard, but it is a two step process (unless you have SP specific shoes). You have to attach the base plate to the shoe, and then attach the cleat to the baseplate...still takes only a few minutes...but if you need to adjust the position of the cleat, you have to take it off, then adjust the baseplate.
Walking was an issue for me too...my building has marble floors that don't agree with metal cleats. I also had to get some rubber cleat covers to put on to walk through the lobby.