My dad bought this hard drive for me at a electronics store a little while ago. I am using it to backup my computer as well as store documents, pictures, and music. I also have a collection of freeware apps .exe files that I store on it.
The storage capacity of this hard drive is huge. I am currently 15 GB of the 500 available, and I doubt I will be able to fill it up for awhile. In that area, I'm completely covered.
The portability of this device is okay but not great. It's small enough to make it easy to slip into a backpack pocket or laptop bag, but you won't be able to stick it into your pocket like some smaller hard drives.
The speed of the my book is also good but not above-normal. It has a 2.0 USB connector but no firewire or SATA, so you can get an okay speed for transfering information. However, don't expect this to be a speed demon; you won't want to use this hard drive to install a operating system or anything similar that needs a fast transfer rate.
Overall, this is a good solid hard drive that can store a ton of info. If you need something like that, go for it. However, it does not have any unique features or any specifications that stand out among the many other competitors.