I have used cheap card readers before, and if you are moving a few hundred digital pics for example, it is not unusual to have a bunch at random be damaged, or even be missed, or have the transfer stall, or just quit.
It has happened to me a number of times, and I was present when it happened to MAVIC as well.
I have one of the SanDisk Extreme USB2 readers now. Their FW reader is even faster.