Flakes are often Job Hoppers. Not all Job Hoppers are Flakes.
Correlation, not causation.
Also, I'd like to see some objective stats here like "do companies with lots of job hoppers do better or worse, here is the data"
Vivek Wadhwa cited in his studies job hopping as an aggregate positive for the economy of silicon valley and its emergence as the prominent startup hub.
http://techcrunch.com/2009/10/31/the-valley-of-my-dreams-why...
Finally, someone taking a shot at that misconception. Just because some people advance their career and improve their conditions by changing employers doesn't mean they're unreliable or incompetent.
Quite often it's the competent people who get sick and tired of a crappy job, widespread incompetence, excessive office politics and stuff like that and they decide to move on. They tie the loose ends, dot the i's, cross the t's and start looking for a better opportunity.
It's not just the startups that mislead people, either. It's just that a big company will lie to you about other kinds of stuff.
Are you treating your employees fairly? Do they feel like they're contributing, or are they writing dead-end code?
You know when they will leave for a new job - when you start treating them like trash.
1. The best people will quit.
2. The median people will whine and make the office a miserable place.
3. The worst people will put their heads down, terrified that they will get fired or laid off.
Consequence? The best people still in their chairs will be the ones with the lowest morale.
The odds are that they won't be around long, and that doesn't mean they're a bad person or someone who can't get things done.
OTOH, the correlation != causation thing is huge as well. One of the reasons some people stay for long periods in one place is that they aren't that marketable because they really don't do much. Nobody is taking them out for coffee on a regular basis and gently trying to poach them.
Sometimes the people who move most often are the ones who have the most choices. Sure, you can label them as "lacking loyalty" or some such, but you cannot assume that those who don't move are automatically loyal. They simply may have stayed in one place because they had very little opportunity to advance by moving.