Well, if you check out the specifications for the drive that Sony uses in the TR, you’ll see that it can withstand quite a bit of Gs (actually exactly 1G) even while operating. Despite being a little performance challenged compared to 2.5” models, the 1.8” model was designed for taking bumps. The 1.8” models can take a little more shock compared to their 2.5” cousins. Heck, it’s the same model used in the iPods and I see people running with those on a treadmill at the gym. There’s plenty of shock there.
Unless you’re going really offroad on big rocks or going rally driving where there’s a chance the TR would actually drop then you shouldn’t worry. If you’re simply on the road then it’s not a big deal at all.