Small form factor allows it to fit in a tight ...
919608
Small form factor allows it to fit in a tight space. Haven;t had to use the backup battery feature yet, I'm sure the thunderstorms of spring will bring with it a few power outages that will test the product.
2113484
The WD My Passport Slim 1 TB Portable Metal External Hard Drive is a portable hard drive with the thinnest and smallest form factor I've ever experienced. It is about half as thick as the standard sized My Passport 1 TB drive and ever so slightly smaller in length. This thin form factor allows the Passport Slim to nearly mimic a USB flash drive in portability and makes it easy to stack in tight spaces. Despite its small size, the outer metal casing is robust and strong. This drive is very well protected. The metal case is cool to the touch so that even after extensive usage the drive never seems to get hot. Adding files is a simple drag-and-drop procedure although the back-up software included on the drive enables you to copy your files on the fly. USB 3.0 transfers are fast and efficient and the drive is very attractive to the eye. Even if space is not an issue, these qualities make this drive a good and secure investment and easy to recommend.
4569215
Smaller than I thought it'd be, but that turned out to be a good thing - it fits neatly into my computer. The air flow coming out of the back is quite strong, so I would assume it does its job. My only problem is that the metal bar doesn't cleanly fit with a larger motherboard, which required some toolwork. Not a huge drawback, but I'm sure I'm not the only lazy person on the planet who just wants things to get in on the first try.

If you know what I mean. Wink wink.
2812139
Small, compact, and holds everything I need to keep secure with room to spare.
2394852
Looks good.  Small form factor.  About the same size as a Logitech Unity receiver.
3240525
This is very small, at 3.4 x 2.7 x 0.7", and has a wrap-around USB cord that makes it convenient to use.  Too bad the internal 1.8" hard drive isn't accessible/upgradable, but that might make it bigger.

It looks like there will be some competition for this thing in the near future from Plextor, with devices that are thinner (0.5" or 12mm) but otherwise a similar size, though without the wraparound keyboard.
4666956
This product is top notch and very affordable. Small form factor allows for easy storage and transportation.
3575273
Compact size, good performance.  A carrying case would have been an added attraction.
2617191
it satisfies a need, is compact and easy to use
1086366
It's a little on the small side; you can't fit much in it. But, it holds my camera, so I'm not complaining.
3996399
This is now my preferred form factor for USB thumb drives.  Since it fits so snug up against the side of the laptop, there is no chance of snapping it off like a conventional thumb drive.  This could easily damage the USB port on the computer.  You can leave this attached all the time if you want with no fear of it getting snagged.  It also look better left plugged into the front of my Blu-Ray player and DVR.  The only downside is that it is so small it can be easy to lose if it gets away from you.
1222640
I like the form factor - this little battery is compact enough to be convenient but not so small it gets lost in my various tech bags. It is, however, chunky enough that I wouldn't want to carry it around in my pocket. It's handy but not quiet sufficiently small to be ideal for what I really need: reliable, small juice for my 2+ year old phone whose battery is lasting less than a day on average.

Mine does not seem to retain a charge. I charged this when I first got it as mine arrived charged at 2 of 4 LEDs on. I forgot about it for a week and decided to plug it into a charger, despite it saying it was fully charged (4 lights on) before plugging it in, and upon plugging it in it's down to 2 LEDs and charging.

I tested charging an iPad (3rd gen), iPhone 4s and Kindle Paperwhite. They all worked, they all charged up reasonably quickly. The battery lasted longer on iPhone and Kindle charges, of course - the iPad is just a hog.  But it did get the iPad to 100% full (I've had problems with other batteries not being able to top off the iPad).

It warms up, but I wouldn't say it gets too hot. It's actually stays cooler than my phone after an hour-long call.

Pros:
Nice size
Convenient USB mini cable built in
Battery itself charges with any USB mini cable - I used a usb mini to outlet set up to charge it rather than plugging it into my computer
Charged relatively quickly - about 10% per hour on the iPad
Decent capacity - actually had multiple phone charges per battery charge

Cons:
LEDs don't seem to be accurate
Pricy
A good size, but if it were flatter/slimmer, I'd be a bigger fan.
4899251
This size was a little tight, but its performance is quite fine.
374196
I purchased this box to build a small server for my home to handle various tasks including multimedia sharing. The form factor is great and the noise level is quiet low and I have yet to have any issues with cooling thus far. My only real issue is with the 5.25 inch back on this case is not properly sized. I purchased a hard drive cage for this case so I could setup a hot swappable bay using this product:

http://www.amazon.com/StarTech-com-2-5-Inch-Removable-Backplane-SATSASBAY425/dp/B003F5NSA6

The 5.25" drive bay scrapes along all sides of my drive cage and I was unable to get it to slide in like one would expect. I love the produce overall and there is very little to dislike, but for my needs it failed in maintaining an industry standard. The front slot is to standard even if the mounting part of the case is not. My guess is that they only measured against the opening and paid no mind to the indentation along the sides and the reduced height for attaching to the rest of the frame.

Note: I'm having the same issue with an Asus Bluray drive I have from my desktop PC also not fitting in this case.
167432
It's a little smaller than I expected, but it works great in a tight space
2934509
Compact and powerful. Snap in case protects it from scratches.
1695310
small enough to put in the bag with the laptop, fully functional at USB-3 so it's fast. Also works with older USB devices.