Loved this photo so much, I thought I'd have a go too! I got given a "GorrilaPod SLR" for my birthday, and I've found it incredibly useful so far - I now use it as much a my regular tripod!
Here's my version. Not far from home in Leeds, UK. Although we have some good tunnels through the city centre, I opted for an open air shot instead. 21:15 hrs, roof off, in the fresh air
Like the OP said - you'll all be surprised at just how sturdy the Gorillapod is - particularly the SLR verion. Being double safe though, i also had the camera strap trapped between the door and the window, as a fail safe. NO movement at all in mine - I'd happily 'risk' my £1000 camera set up on it again - in fact, I'm going to try some more of these shots when I get time. Time for some mounting on the front of the car I think, for a different angle...