I haven't done anything too awesome, but the potential is great. First off, I have x10 which is pretty unreliable because of the powerline technilogy it uses. With the halx I can turn on and off a couple of RF lights that I bought a few years ago at the hardware store, and it works even when my laptop is plugged in! AMAZING
the HALX uses approximately 0 watts. My power meter only shows whole watts and the HALX reads ZERO.
The HALX hosts a tiny webserver, which I can access from my LAN or from anywhere with an internet connection. It has WOL so now I can wake my computers at home when I am away. I spent years trying to figure out a way to do that without leaving at least one machine on in my house, but my router would not let me pass a WOL packet in from the outside.
I can use my iPod, and with a single HALX web page (home made custom html) I can trigger events in VoxCommando or EventGhost, turn on and off my lights directly, wake any computer in my house, and control my stereo and my TV (using IR blasting). The IR blasting is pretty strong too so you don't need have the emitter directly on the device's receiver (although I do since it made sense ergonomically).
There is a serial output on it too but I haven't tested it yet.
There are a few kinks to be worked out in the North American version still but it shows great potential.