You'd be surprised.
Degrees don't count for much in terms of experience. I've seen people with electrical engineering degrees (from good universities) ask which way the strips are connected on a breadboard. Many, many people go through university and get a good chunk of theory in their minds without any practice.
As for companies - if someone is leaving a well known company, you should ask why. Almost always there is a good reason for it, like moving to warmer climes, family commitments and so on. However, there should always be a fizzbuzz check to make sure the person wasn't let go because they were inept.
As an aside, a long list should also give warning signs if it's in a short period. If I'm hiring a 20-something and they've been through 5 companies I'd be wary. They may be a top notch programmer, but do I want to hire someone who will most likely jump ship in a year or two? Probably not.