I travelled with a large external hard disk as well, once - which also got taken to one side and swabbed for stuff. Internal monologue: OH NO MY PRECIOUS DATA ... Oh, it's just the possibility of it being a bomb they're worried about.
On another occasion, I had fun with my home-made, Arduino-powered dSLR timelapse gadget - it got thoroughly inspected by the TSA. I'd already opted out of the backscatter X-ray whatsit, only for a swab-for-explosives test to give a (false-)positive. Eek. Cue being taken to one side, where they looked in my bag and found the timelapse-o-tron...
To give the screeners their due, they let me go after a few minutes - after I'd heard their complaints about the potential radiation doses they and the passengers were receiving from the backscatter X-ray thingers, and after I'd provided advice on what sort of camera to look into buying for a budding photographer.
Security fun elsewhere: carrying a plastic bag of loose change through the Eurostar security in Brussels (it basically looked like an amorphous, completely opaque lump on the X-ray) - and a random customs check at a UK airport giving a (false-)positive swab for some sort of illicit drugs. Eek.