The US justice system gives great credence to eyewitness identification, and an eyewitness identification will even trump an airtight alibi in court. But according to the most recent data from the National Registry of Exonerations, false or mistaken eyewitness identification is a contributing factor in 36% of wrongful convictions:
Here is a brief CNN clip, featuring cognitive psychologist Prof. Elizabeth Loftus of the University of California, Irvine and the University of Washington, giving some examples of faulty eyewitness testimony: Eyewitnesses Are Often Wrong.
If you would like a real “eye opener” on the subject, I recommend the book Picking Cotton by Ronald Cotton and Jennifer Thompson-Cannino. The book details an instance in which the victim had close, lengthy, one-on-one contact with the perpetrator, and still got the eyewitness identification wrong – multiple times.