Replace pre-emptible instances?
I get the part about running batch stuff off line, thanks for the discount, it's great.
However, why would I expect to be able to spin up a full-price instance immediately after my pre-emptible instances was shut down? The pre-emptive instance was shut down for lack of capacity at some level; if everyone tries to spin up an equivalent paid instance, there is still no more capacity. (With a 70% discount, some bright spark will automate all this for MapReduce work, so in fact everyone *will* be doing this, but it won't scale.)
Auction pricing for spare capacity would work better. I wonder if Google could implement an auction at that scale, it might have other business applications :)