I used to use X10. Then I discovered the hard way that buying low-bidder electronics that plug directly into mains power is a really bad idea: one of the control boxes that plugged into a wall outlet started to get hot enough to create a blackened spot on its label.
X10 is particularly horrible for a couple of reasons. For one I'll quote from the Wikipedia entry:
> In the 60 Hz AC current flow, a bit value of one is represented by a 1 millisecond burst of 120 kHz at the zero crossing point (nominally 0°, but within 200 microseconds of the zero crossing point), immediately followed by the absence of a pulse. A zero value is represented by the absence of 120 kHz at the zero crossing point (pulse), immediately followed by the presence of a pulse.
Command sequences are only 2 bytes (16 bits) long, and for certain commands ("all lights on", "all lights off") four of those bits are even ignored. This means it's quite common for electrical noise to be mistaken for signals.
The other problem is increasingly we have more noisy electrical gear on the line, and more equipment that absorbs/filters the actual signals (UPSes, and pretty much any switch-mode power supply in computers, TVs, etc).
I unfortunately put in a bunch of X10 stuff at my parent's cottage many years ago, and it had this problem. Somewhere between every couple days and every few weeks, all the lights would turn on. Sometimes while no one was there, sometimes in the middle of night when you were sleeping :)
We since replaced it with Insteon dual-band, which uses both wireless and powerline, and it's significantly more reliable (and all those problems have disappeared).
In case anyone's interested, we used this stuff because the main floor is basically one big open concept space, and has entrances on all four sides (deck, sunroom, stairs and front door) and the 'smart' switches avoided having to install a stupid amount of 3- and 4-way switches that were originally planned. There's now a keypad by the front door and one in the middle (between kitchen area and sunroom) that can control everything, and a few individual switches by other doors. You can press 'all off' by the front door when leaving and all 6 or 7 circuits in the main area plus the sunroom, hallway, stairs, and foyer turn off.
That's not true. Current-gen stuff works for me across circuit breakers. I haven't enabled any encryption, though, so it's probably packets in the clear that maybe even my neighbor could get. cringe
That led to a wonderful evening of debugging during which I was convinced someone was attacking my wireless network. I eventually worked out that my powerline adapters had connected to next door's circuit, and his DHCP server was slightly quicker than mine.
I've been running it (or an equivalent ethernet-over-power from another vendor) for years and streaming HD TV over it with no problems.
RF spewing out of the mains wiring is true, but again I've not had any obvious problems due to this.
(I'm surprised that they're allowed to be used despite this, however)
edit: Streaming TV over it in that I use it to connect between a MythTV front and back-end, and haven't had any connection or bandwidth issues that I've noticed. It's been pretty rock-solid for me :)
I've tried multiple different HomePlug adapters at home, mostly to stream Steam games from my PC upstairs to my TV in the living room, and after a few months decided it's just not worth it - sure, "tested" speed is always very high. But when you need to stream 1080p@60fps with minimal latency, it's suddenly not so good. The latency tends to go up and down randomly, frames get dropped, it's just a bad experience. I'm sure it's absolutely fine for browsing internet/watching netflix, but local streaming is impossible - I just have a 30m long ethernet cable running down the stairs nowadays, the connection is always perfect that way.
I've been using it on some cheap ethernet-over-power adapters (Devolo, not "HomePlug" brand) for streaming MythTV recordings of HD UK TV for several years and it's been completely fine.
UK Freeview HD is 1080i though, but it's in a very bandwidth-inefficient container as it's just the transport stream which is sent over the network. I've also played some 1080p content over it with no problem, but most of the content I use is 1080i.
No idea how old my wiring is (house is from 1950), and this is across the distribution board / fuse box too, as it's between upstairs and downstairs in my house. So my experience is completely different to yours and much more positive :)
Back in the day X10 (very simple protocol, on/off/dim, no security) actually worked very well, with only a small delay. It's really horrible that 15+ years in the future it's all still so awful.
It's really, really hard to beat the user-interface (or security!) of a traditional light switch or dimmer. I'd like to have control without getting up, automate some things, or change the colors, but that all comes at a huge cost.
This is possible, but requires different wiring to light switches, to provide power there (which isn't common) and for manufacturers of replacement switches, bulbs etc to care about security.
The former isn't something which is happening yet anywhere that I know of (in the UK at least, even in new-build houses), and the latter needs pressure from consumers which isn't happening for anything in the internet-of-things space yet :/
(edit: don't try to use markdown in HN comments, however automatic it has become for you :)
I think the wiring issue is mainly a UK thing. The standard way of wiring light switches in the UK is live and neutral go to the ceiling rose, and then another two wires goes to the switch which joins the live when on. This reduces the amount of wire needed, which stems back to after WWII when copper was in short supply.
I've just bought an apartment in mainland Europe and the live and neutral go to the switch, and from there two wires go to the rose.
In new buildings (~1970+) I've always seen what I consider the standard: live hot and neutral to the switch. Hot is switched to the fixture, and neutrals from both sides are tied together in the box.
Zwave switches can be build into wall boxes, so you still have the same ui as regular switches, it doesn't need network connectivity, so you get remote control as a strict superset of the regular operation mode.
I use Lightwaverf in the UK, replacing the switches with their dimmers. They do have limitations (can't query the state and mostly doesn't work with led bulbs) but the form factor is good.
(I've not used it so I couldn't say why)