Another thought... I'm not sure if the latest software updates have improved, but the used to be a pain in the arse to get working with a lot of wireless keyboards. If you have problems, go for one thats known to work.
Of course there is a hack to use normal remote controls too, but i've no idea about that as its on my lengthy TO-DO list.
And invest in *lots* of high quality usb sticks! I've been finding them a lot more convenient than USB drive enclosures, mainly due to not having to faff about with power supplies.
The one thing the Pi lacks is holes in the PCB to put a bolt through, so getting a clip-on case to house it, and then bolting that to something is a good idea.
And (oh god, i'm on a roll here!) put it somewhere easily accessible, as RaspBMC likes to do its updates down the ethernet cable, and taking the console apart to get at it will get on your nerves. Or just run a patch cable to a surface mounted socket and have an extra long patch cable that you can thread to your home router... or buy a second Pi that is wired in at home just for updating the SD card. But beware of taking the SD card in and out too much, as the card slot is a bit fragile.
And finally... at the risk of overegging the pudding, add Bluetooth support (I'm working on a BT based file server to copy files from/to phones). And if you really want to go mental, a CD/DVD drive (but, power supply faffing again), and you could probably hack it to control the internal lights and an LED text readout displayed in the back window (for whatever reason).
Anyway, I think we all expect photos when its all done! And a write-up!