I'd love a way to turn on my powered desk speakers, and amplifiers in my living room from the computer. If Media Center could do it automatically when playback started and stopped, it'd be even neater. Is this the sort of stuff you're doing?
Yes, that's exactly the type of thing that this would enable. I just use it for light control in the living room right now (triggered by addins like this one), but in other areas of the house I've installed switches and set them to turn on/off at scheduled times to reduce standby electricity consumption too.
What's the cheapest A/C switch that works with the system?
The GE outdoor switches are the cheapest by far. I picked up a couple when they hit $20, but for some reason the prices of all the switches fluctuates a lot so it's one of those things where you have to watch it for a bit. There are a couple drawbacks to them though 1) bulk & 2) they are the only switch I've used that has a measurable amount of power consumption (1W).