According to various scalability articles on FaceBook, they continually rewrite their software. It's probably been rewritten far more than Twitter has, you just never hear about it because TechCrunch doesn't have a source inside.

In my experience, that's really the only way to do software. It's completely unrealistic to think you'll get it right the first time, and yet completely destructive to go and start from scratch. So you pick your worst problem, rewrite it, then hook it back into the working system without touching the rest. Then pick your next-worst problem, rewrite it, etc.

You've got a point regarding the inside scoop however, Facebook doesn't suffer a global outage on an almost weekly basis either.

Having 10,000 servers doesn't say 'skillful' to me.

Facebook's system is also 1000x times more complicated than twitter's simple message passing system!

For me, Facebook often seems very sluggish and slow - I have a pretty useful 4Meg connection and others sites are fine - maybe 10,000 servers is part of the problem - it seems like a ridiculously high number. I wonder how many transactions/pasge views per second they get ...

Employing people with the skillset to build 10,000 servers and having the money to do so are two separate things.

Twitter has millions of dollars.