Other thoughts on the CatKit?
I got a CATkit and 3 kittens 3 weeks ago. Connecting everything was a breeze. The Arduino itself sits in my office with the CATkit shield attached. I'm running 30ft and 75ft CAT5 cables out to 2 kittens with sensors along a busy traffic lane in the warehouse to the loading doors. These are connected to a kitten each with a 4 channel relay that hooks to a mains powered LED light bar. I suppose plugging PIR sensors into kittens to control the the light relay would be the same idea. These are currently running on the digital pins monitoring traffic and the door activity - when a door is opened (contact switch) I sound a piezo buzzer and turn on the loading bay lights. The third kitten is running an LCD display showing the door open/closed status. This uses SPI over the analog pins.
The CATkit was pretty easy to put together and the pins were straightforward to work with. The other option I was considering to assemble the whole system was wireless, but the CATkit did the job for much cheaper and connectivity/distance/interference hasn't been an issue yet. I've got room on the kittens and plans to get creative and start adding automatic PIR light controllers for the rest of the warehouse. The intention behind this is to turn off the lights when they are not needed in the rest of the warehouse. Its been a neat project and I'm hooked on the arduino now! Looks like I need to upgrade to a Mega soon.