I turned down a job at Google (not 300k but hey, it's Google!) to join a startup. The startup started to sink about 2 years later.
I learned a ton and didn't regret it for an instant. Moved on to a new startup 2 years ago when it became clear the first was a dead end. Google recruiters continued to ping me religiously every 6 months regardless.
Moral of the story: Google, MSFT, Facebook, etc will all still be there in 2 years. Especially if you're early in your career and don't need the cash today, go wherever you will learn the most.
Such a story may or may not make it to HN front page, but it sure is a risk that one has to take. And as pointed out, the offers from Microsoft et al are not going away for smart people. Of course, tonnes of smart folks would have taken the offer and lived happily ever after, so I do admire Tom's guts.