If I may start from your good points:
1.) In a network of 500 million users already are the scaling problems still open?
I would suspect that the biggest scaling problems appeared much earlier.
If somebody knows what are the scaling problems that such an enormous networks faces would be very interesting.
2.) I would guess that top programmers can have top benefits in several companies. Even less excellent programmers could get a decent paycheck in many places
3.) I am not familiar with the demographics of facebook but my gut feeling is that most of the programmers are in their early twenties or mid-twenties. This was also my impression during one of the job fairs that I have attended.
cont 3.) I am not so sure what type of mentoring somebody could get there
Definitely extremely smart peers
At the same time it seems that top programmers are moving to Facebook.
Do they see something in the potential of the company that I fail to see.
I guess the possibility of huge financial success besides the "stockmarket" value that is already established they foresee something else.
2.) I would guess that top programmers can have top benefits in several companies. Even less excellent programmers could get a decent paycheck in many places
3.) I am not familiar with the demographics of facebook but my gut feeling is that most of the programmers are in their early twenties or mid-twenties. This was also my impression during one of the job fairs that I have attended.