Demand, more than anything else, has led to a spurt in the job-hopping phenomenon among techies today.
Those who shift jobs frequently can be classified into two categories: One looking at career-progression and greater exposure, the other who seeks to take advantage of market conditions to make a quick buck.
I would give a techie in the first category a chance to rejoin as he brings some value to the organization. He would be more knowledgeable and have an enhanced set of skills due to his passion. Of course, he has to serve for at least 2-3 years in the last job.
The door for the second category of techies is perennially closed. They are like stockbrokers who move with short-term market movements. The passion levels are very low in this category of job hoppers.
I do believe that job-hopping is a win-win situation for the employer and employee, if both can add value to each other on the latter’s rejoining. Eventually it helps in reinforcing the value offered by the organization to its employees.