I wanted to control devices from my bedroom that were in my living room. I already had the HDMI cable in there for the video and used a Pyramid RF IR extender. This did work quite well although it did miss key presses due to interference I'd imagine. The pyramids used to light up when people used to switch their car alarms on/off etc.
My setup is quite unique. Rather than buying a single Matrix switch I have a regular 5 input 1 output switch plugged into a 4 output Matrix switch.
I got this connected up and it works perfectly over a 10m HDMI cable that's joined to another 2m cable with a coupler.
Be warned though this doesn't work through a Matrix switch. You have to position the injectors only over the length of the cable that goes into the other room. The Matrix switch strips the IR information.
There is a slight issue with the design too. Because the IR receiver cable is positioned on one side it can get in the way if you're using Matrix switches or AV Recievers which have very tightly packed connections that are all at the same level. For me this wasn't an issue as I connected it to the far side so the cable could stick out. The alternative would be to buy a short HDMI male to female lead so it won't get in the way.