What are you planning to use as a controller/interface? I use the HomeSeer ZTroller and love it. I've found that since Z-Wave is RF based, it can be touchy sometimes. With HomeSeer's health function and having it optimize my network every night, I've found my Z-Wave setup (some 20+ devices) has become 99.999% reliable to me. I still have some issues with one outdoor module at the back of my yard which only communicates with one other device (used HomeSeer Z-Seer to view node neighbors). And with this heavy snow and the module now buried, I've had a couple failures trying to poll it. I've also had trouble in the summer when a bush in front of the module got too full I again seen a few poll failures. I could easily fix this by adding another module outside that can see this one and give me an alternate route for the RF signal upon failure. Just haven't gotten around to it.

I do know as an early adopter of Z-Wave (started with Z-Wave in 2003), I've seen and had many issues. Like a module burning out and couldn't then delete it from the mesh causing routing problems and slow performance. Moving a module without deleting it and re-adding it caused performance issues, etc. But now that Z-Wave has matured a bit, and the software can better manage and optimize the modules and network. There are also more devices and manufacturers that you have a wider choice of options available today.