I've had this hard drive for a while now, and it has been nothing but fast and reliable. It's hard to come by portable, external hard drives that are as reliable as this one.
640GB of data storage and it fits in the palm of your hand. It runs very low power off of the USB connection (I can't find anything to plug it into which won't power it!). It never drops out at all, and has never lost or corrupted any of my data.
It's plug and play ability is great, I've never had any problems setting it up or using it on any machine. I've been using it constantly all the time I've had it, and it never overheats, powers off, or randomly disconnects. It's totally silent and generally just gets on with it's job.
My only main disadvantage to it is the cable that comes with it is, at best, pathetic. It's tiny and can be broken far too easily. However I'm sure by now most people have many standard USB cable lying around, or can pick one up for very cheap, so it's certainly not a deal breaker.
It's neither very sturdy or very fragile. As long as you don't go throwing it around in a room with concrete floors you should be OK. It doesn't feel too fragile but then I wouldn't want to drop it on a regular basis.
If you need a portable hard drive, this will certainly do the job. I'd recommend it for anyone who doesn't need a hard drive that they want to drop down the stairs.