It can output 5V at 2.1A making it suitable for charging tablets and other devices.
It comes with a cable that has a clever connector, if snapped together it will power an iPhone/iPad through the Apple dock connection, however if the connector is pulled apart, there's also a micro-USB connection suitable for charging non-Apple products. It's also powerful enough to charge a Blackberry device (which lots of other chargers fail to do).
This really is a useful device and has saved the day on many occasions and it actually does manage to produce a full 10W output.
Online prices vary widely, but it can be had for as low as £12 + shipping.