I always wondered what those Play/Stop/FF/Rewind buttons on my TV remote were for. Maybe you could couple a DVD or Blu-Ray player from the same manufacturer through some obscure and proprietary protocol. Turns out I was wrong about that, and actually there's a standard called CEC which allows to simultaneously control several devices connected through HDMI such as TV, AVRs and Blu-Ray players. Manufacturers use fancy names for it, such as Anynet+, Bravia Link, Viera Link and Simplink. And the good news is that it works with XBMC on the Raspberry Pi!! At least on Raspbmc it just works automagically.
I can now control XBMC with just the TV remote. No more keyboard and mouse :-D. I can even turn the TV and the Raspi on and off together!
CEC support on the Raspberry Pi is such a great feature for a perfect HTPC setup, but it's relatively unknown and underpublicized AFAIK.
Here's a live action usage example.