Spin down
I have a Freecom Mobile Drive XXS (250Gb version) and I'm pretty sure that spins down, it even produces a click which I assume is the heads being parked. Futhermore, it also takes a few seconds to spin back up if it hasn't been used for a bit, more evidence I guess that it does indeed spin down. I presume it also does this natively as I took all the included software off of it (and have never used any of it) as soon as I got it.
In fact, while I'm at it, I thoroughly recommend the Freecom Mobile Drive XXS. While they only have a thin(ish) rubber sheath to protect the drive mine has survived a few waist height falls undamaged. Also, with the entire case being rubber, and not just four tiny little feet like some other drives, it helps ro prevent the drive from being pulled off of surfaces accidentally, by the USB cable; the USB connector will let go LONG before the rubber case slips. Surfaces also have to be tilted to some crazy angle before the drive will slip off too, which helps if having to transport a connected drive on top of a closed laptop lid (not recommended I know, but I guess we have all done it at some point!)
I may be tempting fate now but I've also never had problems with the drive itself either (which in my case is a Samsung part). That may be down to the fact I try to treat drives carefully (I've got a 14y/o 17Gb drive that still works with NO errors!) but this drive in particular gets chucked in a bag and transported everywhere!
Long story short... My next portable HD will be a 500Gb Mobile Drive XXS!
(p.s. I know it may sound like I work for Freecom but I don't. I just think this little drive is great!)