There have been 3 distinct standards in USB development, each backwardly compatible. By this we mean that you can put a USB 2.0 in a 1.1 socket. You should feel free to purchase our USB 2.0 (and next year our 3.0 models) safe in the knowledge that they will work in any computer your client has.
The USB 1.0 which has been around since January 1996 became redundant when USB 2.0 standard was released in April of 2000. It has still had continuous updates up until September 2007.
This is the most widly used USH version. This was relased in April 2000. The USB 2.0 version added higher maximum speed of 480mbits (now called Hi-Speed). Youcan use a USB 2.0 device in a USB 1.1 socket, so even if your client has an older computer this wil be a useful gift.
USB 3.0 supports a SuperSpeed (USB 3.0) rate of 4800 Mbit/s (~572 MB/s). The written USB 3.0 specification was released by Intel and partners in August 2008. The first USB 3 controller chips were sampled by NEC May 2009  and products using the 3.0 specification arrived beginning in January 2010.
NOTE: Our USB 3.0 connectors are backwards compatible, so they can operate in a standard USB 2.0 or 1.0 fitting provided it follows USB standard exactly.