Today I read for the first time in this post over at AnandTech that chipsets for mobile devices such as smartphones and tablets are now supporting USB 3.0. I haven't seen devices on sale yet that make use of it but once they do one can easily spot them as the USB 3.0 Micro-B plug is backwards compatible but looks different from the current USB 2.0 connector on mobile devices.
While smartphones and tablets are still limited to USB 2.0 in practice today, most current notebooks and desktops support USB 3.0 for ultra fast data exchange with a theoretical maximum data rate of 5 Gbit/s, which is roughly 10 times faster than the 480 Mbit/s offered by USB 2.0. In practice USB 3.0 is most useful when connecting a fast external hard drives or SSDs to another device, as these can be much faster than the sustainable data transfer rate of USB 2.0, which is around 25 MByte/s in practice. As ultra mobile devices such as tablets are replacing notebooks to some extent today, it's easy to see the need for USB 3.0 in such devices as well. And even smartphones might require USB 3.0 soon, as the hardware has become almost powerful enough for them to be used as full powered computing devices such as notebooks in the not too distant future. For details see my recent post 'Smartphones Are Real Computers Now - And The Next Revolution Is Almost Upon Us'.
Making use of the full potential of USB 3.0 in practice today is difficult even with notebooks that have more computing power than smartphones and tablets. This is especially the case when data has to be decrypted on the source device and re-encrypted again on the target devices as this requires the CPU to get involved. This is much slower than if the data is unencrypted and can thus just be copied and pasted from one device to another via fast direct memory access that does not require the CPU. In practice my notebook with an i5 processor can decrypt + encrypt data from the internal SSD to an external backup hard drive at around 40 MByte/s. That's faster than the maximum transfer speed supported by USB 2.0 but way below what is possible with USB 3.0.