Part of my security cam project involves setting up a video screen that'll display a live feed of my front door cam (whenever I get around to installing that). I don't want the screen to be running 24/7 so I've been tinkering with making a motion activated IR blaster to turn it on only when I'm around.
I've got the PIR working, the IR code for the power button decoded and reproduced, and the phototransistor hooked up and running so that I can have the screen time out quicker when it's dark vs when it's light. I'm at the point where I can basically put it all together, but I'm holding off a little before I solder things together on a board until I figure out how exactly I'm going to build a little cabinet to hold/disguise the screen.
Anyway, playing around on the hardware side is still lots of fun. The Arduino board is a lot like playing with my old Apple ][, just with less RAM and more disk/non-volatile space. Lots of I/O pins to wire up circuit bits to, and a refreshingly simple API to write code against. I like it.