It probably will last quite a while under normal use, the hdd is designed to handle a fair amount of shock (like laptop drives).

Dropping it does have a chance of breaking it, and the harder the surface or the farther it falls the great the odds of a fatal drop.

But dont live your life worrying about things like this, I for a long time was way too careful with my electronics, but now that I see how quickly I replace them, I know to enjoy them while I still want to use them.

In 4 years a mp3 player the size of a sugar cube will hold your Ipod data in static storage, so why worry about it lasting that long?