I'm exaggerating. My point is that doing some studying spread out over periods of free time is more practical than using a more concentrated chunk of time where I already have commitments.
I'd also argue that your friends are in a "special category" of their own, if they're willing to devote months of study time into getting a specific job.
Getting a job at Google means two major changes for 90% of programmers in US:
1. Doubling the salary
2. Working with very smart people on very interesting problems
Each one is worth a couple of months of extra hard work, if you ask me. But if given a choice of doing a cool project for a week, I'd choose that over drilling on red-black trees.
Sure, it's worth the time if it pays off with a decent chance of a job. What percentage of programmers in the U.S. who aren't already working there have a decent chance, would you estimate?
A better question: given that it takes a month of preparation, and given my current experience/knowledge, do I have a decent chance of getting an offer from Google?
I don't really care what are the chances for an average US programmer. If I believe I have a decent chance, I will go through it, because it's worth it for me.
I'd also argue that your friends are in a "special category" of their own, if they're willing to devote months of study time into getting a specific job.