Those inferior USB cable
Anyone using many external USB device, will find themselves overwhelm by lots of USB cables, similar to devices that require many different power adapter.
Compare to firewire (where Apple get it right) , the biggest problem of USB cables lies on the interchangeability .
Today, there is at least 6 types of connector interface for USB. If anyone take a wrong cable with them when on the field, too bad.
To make things worst, the USB mini-A and USB mini-B connector are pretty similar. If you mix them up, it just won’t work. In addition, an inferior mini-A/mini-B connector, will give problem to the user in the wrong run.
Sometime, the user just found their external hard disk/DVD-ROM/etc devices stop working, all because of a pair of damage USB mini-A/B cable.
So instead of buying a new external hard drive casing/DVD writer/modem/etc, one should just find a replacement cable and give it a try.
Due to quality control issues, it happens that many USB mini-A/mini-B connector happens to be too short for some devices. Sometimes, the connector plastic guidance wear off and no longer give a firm grip to the join.