It's a great solution. Most houses in the US have central heating/cooling so the IR remote isn't an option. Although I have seen that style before.
What I want to do is integrate it directly with the system. Here's an example of a Honeywell connector similar to mine.
http://diyhousehelp.com/how-to/honeywell-4-and-5-wire-thermo...
I've been wanting to do something similar with the units in my apartment (they're similar to what you'd see in a hotel window unit). The thermostat and controls are integrated and I can't disassemble to access them, so I either need to build a rig to push the buttons (hard) and turn the temperature dial or just put a relay at the mains and manually set them for AC\Heat depending on season. Adding a relay to the mains seems straightforward, but it's 220v and I don't want to mess up.
I am using one to turn on/off the mains power of a 12VDC transformer. The nice thing about an SSR with an input range of 3–30V (a common type) is that you can drive it directly (and safely!) from a Raspberry Pi GPIO pin (3.3V).