So has AlphaGo raised its level so far just by continuing with the games against itself? Or did they just throw their entire server farm at it? (Or both, probably.)

Demis said it used roughly the same hardware resources as against Fan Hui?

When playing, yes. Training is a different kettle of fish.

I would bet a mix of both. What will be more interesting is if it ends at 5-0 if we will see AlphaGo vs. Darkforest (Facebook's engine) soon after.

Facebook's Go engine is not remotely close to competing with AlphaGo. In fact, it's about comparable to the pre-existing top Go programs; the only newsworthy thing about it is that it's from Facebook and it uses neural nets.

Since AlphaGo's architecture was published in nature, wouldn't it be somewhat straightforward to reproduce something similar to it given the resources of Facebook and an already existing team of people tackling Go? I would expect other Go software to quickly follow in AlphaGo's footsteps and then build on it, perhaps surpass it by adding some different optimizations.