If you are a mobile type that needs to get their data backed up no matter where they are, you are probably going to be looking for a small, compact external HDD that gets all the power it needs from the USB port. There are a number of offerings on the market that will do that, but some of them are more portable than others. A company called G-Technology claims to have the thinnest one on the planet.
The new USB external HDD is called the G-Drive and inside the metal housing hides one of the thin Hitachi GST Travelstar Z5K320 HDDs. The overall dimensions of the G-Drive are 128.6mm L x 82mm W x 9.9mm H. The aluminum enclosure is recyclable and the thing is designed to look a lot like an Apple notebook. The drive is pre-formatted for Mac users as well.
The drive gets all the power and connectivity it needs from a single USB connection. It is Time Machine ready for backing up using the Mac integrated software. The drive has 320GB of storage and has a 3-year warranty. It is shipping right now for $99.99.